Youtube, diagrams, and practice are the best ways to go about learning. The half-windsor is a good knot for almost any tie. The Four-in-Hand is the easiest knot to learn, but doesn't work as well with really thin material ties (ends up too small).
And keep this in mind:
Tie knots allow the tie to slide up and down on the narrow end. You can always slide it down far enough to take it off over your head. Eventually the knot will end up looking bad though and you'll wreck your tie if you leave it tied all the time... but until you're competent, you could keep a couple ties tied and just rotate them out.
... and if for some reason you find you're totally incapable of tying a tie, there's always the Zipper Tie: http://www.thesilktiefactory.com/zipperties9.html