I'm not sure how to post a picture (or perhaps I can't yet since I'm super-new?), but here is a link to someone else's blog with some good pictures to give you an idea of the process. This is what a seamstress would use, but since my mother and I are both home sewists we help each other instead of having to pay someone!
I would only add to the above tutorial that my legs are so short (I'm 5'3") that on most pairs I've hemmed, I have not left the full amount folded up as shown. I prefer to trim the excess fabric to about 1 cm and then finish it with a serged edge (as you see on the seams of most ready to wear clothing) to prevent any fraying. I can't think why anyone would want an inch or more of excess fabric folded up inside the hem of their jeans.
