Even though this bun looks really hard to do, it's super easy and fairly quick. All you need is 2 ponytail holders (clear if possible), a comb, a brush, and several bobby pins. (By the way, the thing in the far right of almost every picture is a stuffed horse. I was doing this on my sister and she decided to read while holding her horse. Sorry about that!)
The first thing you need to do is to part your hair in the middle all the way down your head. Using a comb will really help, but it isn't absolutely necessary.
Next, pull half of your hair into a ponytail holder and dutch braid the other half. (If you don't know how to dutch braid, click on this link.http://www.wikihow.com/Make-a-Dutch-Braid
Basically, it's just like french braiding, except you pull the strands under instead of over.) Secure the braid with a ponytail holder.
Braid the other half of the hair and secure with a ponytail holder. Then, cross the braids to make an "X."
Take the end of the braid on the left and tuck it into the braid that's attached to the head to form a loop. Use bobby pins to secure the braid. Repeat with the braid on the right. It should vaguely resemble a pretzel.
To finish the braid, you could add a fancy clip or comb. Enjoy!