@ruthless4u For an end user, it's just a matter of fiddling around with the app and figuring out what features and settings get you the gaming experience that you're looking for.
Fire up a game in nestopia and compare it to fceumm. Try a different color pallet. Compare the audio. Change your settings and see how it affects your game. Once you get a hang of things, you can read up on what each feature does and why they exist, like threaded video, audio filters, etc. Why should you use one emulator over the other? Why should you care about performance versus accuracy? And even if something goes wrong, nothing is permanently broken; just start from scratch, look it up online, and figure out what works and what doesn't.
I started using RetroPie to clean those tough bathroom stains that most products leave behind. After realizing that it was intended to be a retro gaming platform, I found that it still outperformed it's competition by a wide margin.
@gotwood3001 If you exit emulationstation with F4, you will be taken to the command prompt. From there you can edit files with the nano text editor. There is a much easier way though to edit /boot/config.txt and that is to use winscp or putty to access it via the network. Read more. Video tweaks here.
@klv74 also make sure you install the emualors for each game system you add ROMs for. RetroPie 4.0x doesn't came with many emulators already installed anymore so the over all file size would be smaller.
Also NES games can be zipped up and will work with most of the emulators but they won't read inside of 7zip'd files. Now the PSX games need to be unzipped and be the BINs and CUEs or I think ISOs will work as well.
PSX games that work well for me are:
Gran Turismo 2 (Arcade Mode)
Metal Gear Solid
Strider 1 & 2
Welcome to the emulation scene! You might want to check where you got the file from and what type of dump (release) it was. TOSEC and Redump are some of the more popular versions of the disc based emulation images you may have.
You need to fine out what extensions are being used within the zipped file. CUE/BIN or ISO etc. This will determine what configurations you may possibly need to make, or whether you can simply drop the image into the roms folder and run it.