Setup Wifi connection
Use wifi to transfer roms over the network rather than a USB stick or Ethernet cable you'll need to setup your wifi- which can also be done from the Retropie menu in emulationstation:

Connect to Wifi Network



Choose your SSID from a list



Type your Wifi Password (may take a moment to connect)



Once configured you will see your IP address



Now you can access Wifi Network. More information see this page

Installing additional Emulators
On RetroPie 4.0+, not everything is installed by default. The pre-made images contain the best working emulators for each system supported by the hardware. This should cover everything most users would be doing. Ports like quake and doom and some other emulators like ScummVM can be installed later.

Software can be installed from the RetroPie-Setup script - which is accessible from the RetroPie menu on EmulationStation. Once there you can navigate to "Manage Packages" where you will see various sections. In each section are lists of packages that can be installed (and it will show what is currently installed). Stable additional packages are under the "Optional" section, with more unstable packages listed under experimental. The packages are ordered first by type (emulators / libretro cores / ports), then alphabetically. By selecting a package you can choose to install it, or remove it. Some packages also have additional configurations.

Transferring Roms

Due to the nature/complexity of Copyright/Intellectual Property Rights Law, which differs significantly from Country to Country, ROMs cannot be provided with RetroPie and must be provided by the user. You should only have ROMs of games that you own.

There are three main methods of transferring roms: USB , SFTP and Samba-Shares.

USB
• (ensure that your USB is formatted to FAT32 or NTFS)
• first create a folder called retropie on your USB stick
• plug it into the pi and wait for it to finish blinking
• pull the USB out and plug it into a computer
• add the roms to their respective folders (in the retropie/roms folder)
• plug it back into the arcade lite
• wait for it to finish blinking
• refresh emulationstation by choosing restart emulationstation from the start menu
SFTP
• Wired (needs ethernet cable)
• Wireless (needs wifi dongle) There are many SFTP programs out there, for windows many people use WinSCP for mac you can use something like Cyberduck

FTP config



Default username: pi

Default Password: raspberry

You can also log in as root if you wish to change more files than just the roms, but you first need to enable the root password which is explained here

Samba-Shares
• if on windows type \\retropie into the computer folder. You can also replace retropie with your Raspberry Pi's IP address

  

• if on MAC OS X open finder, select "Go" menu and "Connect to Server". Type smb://retropie and hit "Connect".

PuTTY telnet client software


(Link to www.putty.org )

• On config window type retropie into the telnet. Or you can also replace retropie with your Raspberry Pi's IP address

  

• Type default username: pi, and default password: raspberry

  

  

Arcade emulation requires a different planning approach than console systems. Please read this entire page before beginning your RetroPie arcade emulation project.
Step One: Choose an arcade emulator

System	Recommended MAME Emulator	Recommended FB Alpha Emulator
Pi 2 and Pi 3	lr-mame2003	lr-fbalpha
Pi 1 and Pi Zero	mame4all ( NOT lr-mame4all)	pi-fba

Other MAME and FB Alpha emulator versions are also available in RetroPie. Please be aware that earlier versions generally run faster than later versions, but also support fewer games.
Step Two: Use the right ROM Set Version
Start with a full Non-Merged ROM collection (not an individual ROM) with the exact MAME or FB Alpha version number for the emulator you wish to use. An incorrect version or missing files will cause most or all games to immediately exit. In other words, lr-mame2003 will only work correctly with a collection of MAME 0.78 ROMs, mame4all will only work with a collection of MAME 0.37b5 ROMs, and so on.

Arcade Games and How to play them – A short non-technical guide.
I am posting this to supplement the excellent and detailed information in this thread on MAME emulation. If you find that too complex, this will hopefully get you started. Remember, Arcade emulation is not straightforward and will require at least some reading on your part. If your are totally new to the retropie experience and your roms don't load then read on.....

Arcade machines from the 70s, 80s and 90s contained a variety of electronic components to enable the user to interact and play the games. The machine code for all these games was stored in small ROM chips on the arcade machine motherboard. Over time, the code became more complex and powerful together with the size and capacity of these rom chips. The ROM files that we use today to play these games are a copy of all the data inside a given chip taken from the original arcade motherboard. Since arcade machines are very complex and contain many rom chips, emulator authors needed to obtain the data from all these different chips before they could write software that could emulate the game correctly and provide the gaming experience that we all treasure today.

Now you know what a ROM is, you will need to acquire some so that you can play. This is what causes most frustration. It is all about the ROMSET VERSION. If you do not know the version, you will not know what emulator to select. These ROMS are NOT  universally compatible with the emulators that are available. Many people assume that they are and as a result have a frustrating time. You will read posts where people say MAME is rubbish, it's hit and miss, go for it, see what happens etc, etc. It is never hit and miss, it is an exact science. It will work if you have the correct romset. It is also very important that you do not download single ROMS of your favourite game from a random site and try it in multiple emulators until it works. The fact is that it might work if the ROM has not changed much over the years but most likely it will not work and you will be left bemused and frustrated again. Now due to legal reasons, the various locations of where ROMS are located cannot and will not be shared on this site because it breaks the forum rules. However, Google is your friend here. You must treat Google with the respect it deserves though or it will point you towards incorrect, unfriendly and time wasting locations that will add to your frustration.

Step1: Decide on the ROMSET you would like to acquire. To do this, look at this page and the list of games under the compatibility list.

Step2: Use google to search for a “reference set” of your chosen version, e.g. 0.78

Step3: Download the set. WAIT! Before you do this, be aware that unless you have obtained the right to use the rom dumps from the copyright holder, you are technically breaking copyright law.

Now if you have managed to acquire a “reference set” successfully, all you need to do is transfer the set to the arcade rom folder of your retropie setup. This means copy the set from your pc to the raspberry pi location:

/home/pi/RetroPie/roms/arcade

Step4: Reboot the Raspberry pi and now the games will appear under the Arcade logo.

Step5: You need to learn about the run command. It allows you to select the emulator that will run a particular rom from your Arcade folder. The emulator that you select in here must match the “reference set” that you downloaded according to the information on this page. If not, you will be booted back to the menu after enduring the dreaded black screen. Here is an example:

Let’s say that you managed to download a 0.78 “reference set” and you placed it in the Arcade ROM folder. The default emulator for the Arcade folder is lr-mame2003 so they should launch just fine. However, you might have other reference sets on your pc hard drive such as Advance MAME that work better with vector games. You could put some of these in here too with your 0.78 set but they will not launch unless you select Advance MAME in the run command for those “new” additions to your arcade folder rom collection.

Now you should be enjoying your arcade experience. If not, you have made a mistake with regard to the emulator and it’s required roms – you have a mismatch. You should now consult the wiki for more detail on configuring further if you feel like it and the importance of bios files if you are craving more detail – these should be in your “reference set” already so no need to worry about them right now. Games will launch.

Step6: Some early games require samples to be present for sound effects, these need to be acquired and placed in the correct place. They also need to be samples that are the correct version, e.g. for 0.78. A quick Google again will suffice on where to place them and where to find them.

One final note. There appears to be an abundance of 3rd party images floating around that are pre-configured with full romsets. If you get one and can't work it, no good posting on here as nobody will know anything about it and it's illegal. You should consult your supplier for ongoing support but you will probably be disappointed as they have stolen your cash since retropie is free.

Artwork: A4 size pager printing

Artwork installation

Login retropie by telnet or terminal software.

Configuring Runcommand via RetroPie-Setup

Following step for disable Launch menu when MAME run.

The runcommand configuration option in the RetroPie area of Emulation Station.

Retropie (ES menu)
RUNCOMMAND EDITOR
1 Launch menu (Disable) <--- set to disable

Login retropie by telnet or terminal software.

Login retropie by telnet or terminal software.