Sometimes just a red LED on the board turns on and the console doesn't boot. In that case, it usually helps to unplug the power cable, wait for >10 seconds and plug it in again (and repeat if necessary).
Using the Interface
Navigating and starting games should be self-explanatory as there are some hints on the screen.
Please don't mess around with the RetroPie configuration, just play some games or enjoy some demos...
Exiting a Game
Select + Start should do the job.
Use the menu of EmulatorStation and chose Quit -> Shut Down System.
It doesn't really matter if you unplug the power cable afterwards, but if you want to do so, please do it after the screen is off and only one red LED on the board remains on.
If the console becomes unresponsive at some point, please be gentle to it:
If you are in a game, press Select + Start.
Wait for a few minutes.
If the problem persists, unplug the power cable.
If you power off the console by unplugging the power cable, plug it in again and shut down the console properly after it boots up. (This will give the console the chance to do a file system check during the boot.)
Emulator and ROM Management
RetroPie actually supports a lot more emulators than just NES and SNES. However, before using a new emulator one has to make sure that our old Raspberry Pi has enough performance to run it decently and we have a suitable controller for that emulator. Feel free to dig the list of emulators RetroPie supports and find some new ones which fit to our setting...
The ROMs are located in /home/pi/RetroPie/roms, sorted by emulators. You can manage them by accessing the SD card directly or use a convenient RetroPie feature to add new ROMs from a USB stick (as described in the RetroPie documentation):
Make sure that the stick is formatted to FAT32 or NTFS.
Create a directory called retropie on the stick.
Plug it into the console and wait for the blinking (on the board and/or on the stick) to finish.
Pull the USB out and plug it into a computer.
Add the ROMs to their respective directories (in retropie/roms).
Plug it back into the console.
Wait for te blinking to finish.
Refresh EmulationStation by choosing Quit -> Restart EmulationStation from the menu.
Please be careful about the power cable and try not to unplug it while something is running on the console. The SD card is very sensitive and the file system is likely to be corrupt after a sudden power outage.