Question about modding

Hi! I hope it's ok to ask this potentially stupid question here: how do you manage mods within game? I've seen that people have this mod menu they can access to change things while playing, but even though I've got mods and they work perfectly well, that doesn't show up. I sort of assumed that maybe one of those lib mods was needed (repo lib or menu lib, what are they called), but I've tried both of those and nope, mods are just not showing up in the menu for me.

This is the first game where I've ever tried to use mods, so I'm new to this stuff....