Here is a SUPER easy hair tutorial on how to do a low bun. I love this hair do because you can pull it off as a messy / classy hairstyle that works for ALL kinds of situations. You can be at a fancy event all dressed up, or throw on a sweater and jeans, and either way it dresses for the occasion - and all you need is a few bobby pins!
Separate your hair in the back into two pig tails. Twist them, and knot them. Pull tight.
Wrap around the two ends and stick them into the knot. Add bobby pins on top of the bun, sticking them down into the bun to secure.