Overwhelmed to the Point of Giving Up (Again)

[Paddy™]

This is probably my third real attempt to get into modding SOMA, and I'm still as baffled as I was in 2015. I'm stuck at the very beginning of the process, and was hoping someone could put me out of my misery and just tell me what to do so I can actually start building levels etc. Feel free to patronise me, treat me like an absolute dumbo!

Get me from "nothing" to "having a mod/map I can playtest/edit". I'm OK with the level editor, so don't worry about that part. I just don't know if I should be saving my map in a separate folder, or if I should use the "mods" folder inside the SOMA directory (the editors keep opening the main directory, so I dunno). When the tutorials talk about editing config files, I don't know if I should be editing the main files, or copying them somewhere to be edited separately, or what. If I'm playtesting a map, does it mean I can't play the main game without unediting the config files again? Do I have to manually build a directory structure to mirror that of the main game for the mod to work? What's CodeLite for? Why can't I just use Notepad++ to do scripting, for instance?

This is the sort of stuff that's making my brain ache, just basic concepts about where things are supposed to go, and the wiki/videos are just making me even more confused because they seem to presuppose a level of knowledge about this stuff that I don't have.

So, pretend I'm a foreign exchange student with very little English and whose mother drank heavily and constantly rode poorly-maintained rollercoasters during pregnancy.

Thanks for your help/patience, lads