How do you start or sing up for gymnastics?

You can probably look in a phone book or the internet to find a local gym in your area offering gymnastics. Some gymnastics facilities offer more than gymnastics as well. The gym I coached at offered, dance, gymnastics, tumbling, cheer-leading, martial arts, and swimming so it may not be listed directly under gymnastics. Then you can call their office or just go directly to the gym and ask to be enrolled in gymnastics. Depending upon how reputable the gym you participate in, it may be more expensive than others. Figure out what is most important to you: cost, friendliness, quality etc. and pick the right gym. Then you will choose when you want to do gymnastics and start as soon as they let you.