Your printer should spell this out for you in easy to understand terms. If not, find another printer
If you are looking to just know what your talking about when you talk to your printer.....honestly, it's better to go in not knowing too much otherwise the printer may think you know everything and gloss over the important steps.
To answer your questions (without more specific details on your project).....An 8.5x11 catalog is 11x17 folded in half (Each 11x17 is 4 pages).
Now the variables begin...Self cover, Plus cover, etc...............Talk to your printer!!!
There are 3 types of people....Those who make things happen......Those who watch things happen.....and those who wonder what happened.