This is one of those essential man skills, up there with shaving, and hunting a wild boar with a knife and a stick.
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.....
Lift the collar of your shirt. Place the tie around you neck.
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
Cross the wide side over the thin side, bring it around the back, and return it to the front. You'll have made a full loop when you're done.
Step 3: Four in Hand: Up and Through
Pull the wide end up behind the loop you just made, and through the two halves of the tie, as shown in the first photo.
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.
Step 4: Four in Hand: Fishing Touches
Pull the wide end of the tie down, tightening the knot. Now grab the knot, and the thin side of the tie (the one in the back) and pull upward on the knot to move the tie higher on your neck.
Step 5: The Mystery Knot: the Beginning
Begin the Jeff knot just like the four in hand. In this case, since the knot is a bit thicker and uses more of the tie fabric, you'll want the thin end to be higher up (ie, the wide end will hang lower) than it did for the four in hand.
Cross the wide side over the thin side, then bring the wide end up behind the thin side and over.
Step 6: The Mystery Knot: Make a Loop
Bring the wide side back behind the thin side and back around front, making a loop.
Step 7: The Mystery Knot: Completing the Knot
Just like the four in hand, bring the wide end up behind the the loop, and between the two halves of the tie.
Put the wide end through the front part of the loop, and pull down.
Just as in step 4, grab the knot with one hand, the thin side with the other, and pull the knot up to your collar.
Step 8: What to Do With the Back Side and Notes on Length
In all cases, the tie should hang at roughly the belt line and the knot should be fairly flush with the collar. As I previously mentioned, you'll use the position/height of the thin end relative to the wide one to determine final tie length, and it may take a few tries to get it right. Even after 12 years of wearing ties, I rarely do it perfectly the first attempt.
The back of the tie should never hang below the front. That's a fashion no-no. If no matter what you do, you can't get the both the tie to end at the belt line and the back of the tie to be shorter than the front, your tie is too long. Get a shorter tie. (They do come in different lengths.)
Additionally, the back of the tie should never be flapping around. People used to use tie pins or clips to make sure of this, but most ties today either have a specific flap for the back part of the tie, or a label you can use in its stead.