You have to be able to throw a football, of course, and you have to be able to read, understand, and remember a complex playbook. That is the most important part.
The best way to become a quarterback is to study the position and as people always say practice practice practice. Another thing that you could do is to attend a football camp in your area.
You can become a QB, or Quarterback, by practicing. Start by going outside with your friends and throw a football around. Slowly build up to throwing a spiral, and later throwing to a target.