If you click in the image above it will take you to an article that shows various ways of tying your belt.
Please ignore the martial art style or the grade the article advises for a particular method.
Whatever way you choose should be acceptable in most dojo (training room).
The knot needs to be practical. Its main function is to keep your gi top closed. The position of the knot is important for safety reasons, you need to keep the belt centrally at the front, near the belly button. You don't want the knot to dig in your back or side as you perform breakfalls.