First time adding mods to BG EE, what do I need to do?

So after reading a lot of the threads on here this strikes me as a resoundingly stupid question, but I've installed some mods in the past which have messed up the whole game so I want to be sure I am careful with Baldur's Gate EE. I'd like to know exactly what's involved with installing a mod for the game. I've read a lot about WieDU and override files, but I guess I'm just not exactly sure how I'm supposed to implement mods for Baldur's Gate EE (not worrying about BGII EE yet). Right now I have the game through Steam. Do I need an override file for any mod? I know this is sort of vague and probably very easily answered, but as someone who has never successfully modded a game before, I don't really know what I'm doing. Any help y'all could give me would be great. Thanks!