I mean that the ActionReplay code for a particular cheat is identical to the GameShark code for the same cheat.
Here is the ActionReplay code for Infinite Gil:
Here is the GameShark code for Infinite Gil:
I can't help you on the actual usage of cheat codes, because I've never used one. I don't like to use cheats to beat games. The closest I've come to cheating on the PS1 is using the save state feature of the emulator to get quicksaves - and then I only use them to pause the game so I can quit without having to get to a save point.