Some excerpts from the USAPA.ORG website:
Some players have already been given tentative ratings based on previous tournament results, recommendations by tournament directors, and other player opinions that we have sought. More players will be given ratings as we get more tournament results and time permits. You may find out if you have already been assigned a rating by going to the Ratings section of the USAPA website.
If you don’t have a USAPA rating, then you may rate yourself when you enter a rated tournament for the first time. Your initial self rating must be approved by the tournament director. Depending upon your tournament results, your self-rating could be changed if it appears to be obviously wrong.
A non-rated player may establish a rating in a rated tournament. However, this is always subject to the Tournament Director’s Approval. If you are unrated, you may enter the rating division of your choice based on your ability relative to other players that you know. Here is a table showing the various ratings and what they mean as far as USAPA is concerned.