What exactly are protals and what do they do?

Well, take a look in the tutorial section... there are also a few video's there. if you look at these tutorials, you will get ur answer explained

Basics:

Portals devide you map into small parts, called "cells". If you're in one cell the engine calculates which cells you can see and, based on that, draws only the cells you can see.

Proper use of portals will raise FPS on your map, because the engine isn't busy drawing everything. Overuse, or too many cells, will cause the engine to have to caculate too much instead of drawing the game.

Is there anywhere else I can download Wyatt videos on portalling as I have to wait more than 8 hours to download them from here.

No.. it's a big file.. which takes time.

Become a member and you'll get higher download speeds.

but.. there is also a very good written tutorial along with an example map in the CoD tutorials.