Here's a bit of practical origami for folding a little handle for a take-out bag. I reverse-engineered this from a neat trick done by a waiter at a Chinese restaurant.
Step 1: Fold #1: Right Triangle
This first fold is easy. Fold the upper portion so that you have a 45 degree fold. The image shows the fold for making a left-handed handle. (Mirror-image it for a right handed handle.)