Hi I would know what are the main functions to edit the PSP RAM ?
There are plugins like CWCheat or nitePR which edit PSP ram, and I like to make a PRX containing a PSP code made by me so I need to know what functions I have to use.
If you have to ask, you aren't capable. There are NO functions that "edit" ram. To even say such a thing shows how little you know about programming in the first place. Please go learn to program elsewhere, then come back when you don't need to ask questions like the ones you just did.
There are lots of open source prx's out there. Look at them. As for "editing" ram, read the C manual on using pointers. That's plenty to get you going.