Alright, so first of all you will need to buy the elastic. I bought 5/8" Fold Over Elastic at JoAnn's. The only color I saw there was black (which is kind of boring, but oh well).
You will need sharp scissors for this project! Measure out 9 inches of the elastic & cut it there. Then, you will tie it in a knot. You're done & have been a hair band!
Here's my finished project (& my very freckly arm!)