If you have long hair, but no one around who will braid it, or you just want to be able to do it yourself, here's how to teach yourself.
Pick a spot on the floor close to a couch or chair. Sit with your back to the couch or chair. Lean against the couch or chair for support.
Brush or comb out your hair and separate into 3 long strands -- left side, middle, right side. If you want you can make a pony tail at the base of your neck to start, but I would recommend trying to doing this without making that initial pony tail. It's more challenging but will give you better results in the end.
Grab the 3 strands in your hands, keeping the hair as tight as you can make them, close to the back of your neck, propping up your elbows on the chair or couch as needed, when your arms get tired.
To do a basic 3 strand braid, remember that you are basically switching the middle strand with the right, and then with the left, in a consistent pattern, with the left and right strands always being passed over (not under) the middle strand.
When you get to the end, secure with a rubberband.