That's a good question, actually.
I'm just going t suppose that Werivar has both graphic and data files. These should simply be put into their appropriate folders, of which one will have to created, the mod's data folder.
That the gist of it, a step-by-step would be:
I don't have Notrium installed, neither do i have the intrawebular capacity to download Werivar.
But it shouldn't be that difficult... uh... okay... now, you should have a "data" folder. In it should be "default" and "tutorial" (i think), in either of those a bunch of files named with stuff about weapons and climates and stuff with a .dat extension (they're actually just simple text files.). Now, you need to go back to the "data" directory and next to "default" and "tutorial" create a folder named "werivar" (or anything, really, this just decides how the name of the mod will show up in-game), and copy all the .dat files there.
Now. I don't remember what the exact name of the folder which hold graphics is, but it should be fairly obvious (It's a folder with graphics in it ). In there, create a folder called "werivar" aswell (it shouldn't have any other folders, just full of pictures) and put all of them graphics there.
However. It might not work. If so, try putting the Werivar graphics in the main graphics folder.
If it STILL doesn't work, i've made a mistake somewhere. But no worries, i have said nothing that can't be easily fixed and people smarter than me may or may not post before you even get to read this one.
PS. Yeah, i know i could've made this post ALOT less text-heavy. But whatever.