Hehe, I felt the same when I first started it. First click "load module (Warband)' in the top right corner, and select whatever which mod you want to tweak (don't worry, it has native there as well, it's kinda hard to miss), then you'll need to select where on your computer it is
(C: -> Program files (x86) -> Steam -> steamapps -> common -> MountBlade Warband -> Modules For Steam users)
A loading screen will pop up once you've double clicked it, just wait for that. Once it's finished you should have a list of tweaks. simply click and follow what the screen tells you.
Even if it doesn't have the tweak you want, it's decently fun to mess with.