Here is a video of Mr. Arthur explaining how to tie your uniform and belt.
The video is mirrored to make it easier to follow along.

The Belt is tied in a square knot.

If it’s your first try make sure that your ties have been properly secured, and that the left side of the jacket overlaps the right. (fig. a. & b.).

The next step is to fold the belt in half; to determine the center, then place the center point at the front of your waist (fig. c.).

Wrap each end of the belt around to your back (fig. d.) then continue around to the front. You can match the ends of the belt at this point to ensure evenness. Taking one side of the belt in your left hand and the other in your right cross the right part over the left and then wrap it underneath both pieces of the belt (fig.e.). The new left end goes over the top of the right (fig. f.) and is pulled through the loop created (fig. g.). Taking both ends pull the belt out to your sides to tighten your knot. It is considered a matter of pride for the ends of your belt to be of equal length after the square knot is neatly tied (fig. h.)