Just look it up on youtube. There's a whole bunch of vids. for finding skulls and terminals. The thing that sucks the most is that you can't find any skulls by using the mid-level save points, you have to start each level from the beginning for the skulls to appear.
I wish I had tried to find those things when I played H3 for the first time. Now I'm playing on Legendary which makes staying alive to find the skulls and terminals just that much harder.
Anyway, good luck.