This page of the website details information about the format of the various AAU National Championship Tournaments. 

All tournaments follow the same basic format, although the details of the format vary by age group and/or Division:

.  Pool play.  Teams grouped into a pool of generally 4-5 teams play each other in a round-robin format with standings kept and the top teams advancing to bracket play

.  Bracket play.  Teams are placed into brackets based on their finish in pool play.  In either single-elimination or double-elimination format, the teams play eachother until a champion is crowned.