One of the best features of your RetroPie system is the ability to, at any time, SAVE and LOAD your game progress. It's super easy to do.
SELECTING A SAVE GAME SLOT
Not only can you save your game whenever you want, but you can have MULTIPLE save game slots so that you don't have to overwrite your previous saved game (say, if you wanted to save your favorite part of a game!). To select your save game slot, simply press and hold SELECT on your controller and press LEFT or RIGHT on your d-pad to move back and forth through the save slots. You'll see a yellow message in the bottom left corner telling you what slot you have selected.
SAVING YOUR GAME
Again, super easy to do. Simply press and hold SELECT and then press R1 (the right shoulder button). You will see a yellow message appear in the bottom left corner telling you your game has been saved in whatever the currently selected save game slot is.
LOADING YOUR SAVED GAME
Just as easy, to load your saved game simply select the save game slot you want to load and again, press and hold SELECT and then press L1 (the left shoulder button). You'll know it worked because it will almost instantly load your game from where it was saved but you'll also see another yellow message in the bottom left indicating that it loaded the saved game.
EXITING THE GAME
When you're done playing you'll need to return to RetroPie to either select another game or to shudown your system. To do this, press and hold SELECT and then press START. This will quit the game and automatically return you to RetroPie.
Here is a useful Video:
The buttons and methods used in this guide are the DEFAULT settings. If you have configured your own controller (or reconfigured the ones that came with your system) and have assigned different buttons, you'll need to keep that in mind when following this guide.
Also, not ALL emulators support the save/load functionality or use the same button combos to quit the game. For more information, search google for "name of system retropie".