What you needWorsted weight yarn, and a crochet hook
1. Chain 30 (or more for larger buttons). Single crochet in the 2nd stitch from the hook, and in each stitch of the chain.
Fasten off with a long yarn end, and thread the yarn end into a yarn needle.
2. Place the needle on your work surface, and roll up the strip from the opposite end. Pass the needle directly through the roll back and forth several times to totally hold all the layers together.
3. Use one of the yarn ends to sew the button onto your project.
See a demo here: