cant understand raycasting

i tried understanding the premandi tut, i got it but couldnt implement it.

the most readable code i found was.

http://dev.opera.com/articles/view/creating-pseudo-3d-games-with-html-5-can-1/#comments

but his comments and explanations a vague i got stock with the castRays and castSingleRay.

i also had a long qbasic tut (i have qb on my win7).

cant find any good book about it (couldn't find any download so maybe ill buy one).

i really wrestled with this interesting subject the hole week and coldent reach full understanding.

what do i need to learn to understand it?

please can anyone help me ill give you more detailes if you need more.