Okay, the last one isn't as essential, unless you happen to be named Rambo and are forced into the hills by a malicious sheriff, but you really should know how to tie a tie.
I'm going to teach you how to tie the two most basic knots, the four in hand and a mystery knot that I thought was a windsor, but which isn't. It is however better than both the half and full windsor, as it's more symmetrical. Upon further investigation, it seems closest to the Pratt knot, but unless someone can tell me differently, I'm just going to call it the Jeff knot.
Step 1: The basics for both knots.....
If you're right handed, you'll probably want the thin side on your left. If you're left handed, the opposite.
The wide end should hang lower than the thin one. How much lower is going to depend on the length of the tie, and on your height. Ultimately you'll get the feel for it after bit of trial and error.
Step 2: Four in hand: the beginning
Step 3: Four in hand: up and through
Now take the wide end of the tie, and push it through the front part of the loop. When you're done, it should look like the last picture.