What specific files do a PSX emu (e.g. ePSXe) require to run a game?

[Double44]

I've been mowing around these forums and cannot find a direct answer. It would be helpful if this FAQ could directly tell us the filetypes needed for a PSX emulator to run a game. I've weeded through so many posts, and have managed to rack up questions faster than answers.

I'm trying to play the games below on Android using an app called RetroArch; a free emulator w/multiple emulators from various consoles, or "cores" as they call it. I need to know which files to dump on Android in order for the "ePSXe" emulator/core to run the game(s).

The ROMs I've downloaded/unzipped from EmuParadise include various files, and I'm not certain which games are 100% ready to play and which ones are not. It seems I've got an assortment of flavors here, does it really got to be this complicated?

MediEvil 2
1) CCD
2) IMG (disc image file)
3) SUB

Castlevania Symphony Of The Night
1) 7z
---1) BIN.ECM
2) APE

Castlevania Symphony Of The Night (a different version)
1) BIN
2) CUE

Twisted Metal 4
1) CCD
2) IMG.ECM
3) SUB

Also, can someone give an explanation of each filetype, including the difference(s) between an ISO and a ROM?