Go on Youtube (or Google) and just search for 'hair bun tutorials' or 'messy bun tutorials' and you'll find plenty of videos on them. But here are two that I've found pretty useful; one that is really simple (here) and the other, a little more tedious but I think it looks less sloppy and closer to my updo (here).
Alternatively, I think these pictures are good enough to illustrate how to get a nice fluffy bun :)
