There are four principle knots used to tie neckties. In rising order of trouble, they are:
the four-in-hand knot. The four-in-hand knot might be the most widely recognized.
the Pratt knot (the Shelby tie)
the half-Windsor tie knot
the Windsor tie knot (additionally needlessly called the "full Windsor"). The Windsor tie is the thickest knot of the four, since its tying has the most number of steps.