There are dozens upon dozens of ways for you to tie a necktie, and some of them are quite interesting, and fun to look at, but there are really only three knots that you need. Every other knot is completely superfluous, or, sometimes, completely ridiculous and unnecessary. The three knots that will get you through every situation imaginable (at least the ones where you are wearing a necktie) are: The Four-In-Hand, The Half-Windsor, and The Full Windsor. Which know you use depends mostly on the shape of your collar. For a point collar, you will typically use a smaller knot i.e The four-in-hand. For a semi spread collar, go with a half windsor; and for a full spread, use a full windsor. Remember, all ties should reach the top of you belt buckle (or the area where it would be), and should have a dimple.
The Full Windsor
I highly encourage you to learn as many knots as you want, just know that these are the only three that you will ever really need.