Each region hosts "elite Testings" or competitions- usually 3 or 4 per year. A gymnast who is starting out as a "pre-elite" or "hopes" athlete must "test' (compete) both a compulsory routine, and an optional routine for each apparatus. Hopes athletes are ages 9-12, and the FIG requirements are slighly modified in the optional competition. The pre-elites (ages 13-15) or international elites use straight FIG rules (like the olympics).
There are certain qualifying scores for hopes, pre elite and international elite. Hopes and pre-elite scores are lower, and they are trying to qualify to the American or US Classic competition. From there, if they do do well, they can be put on a National Training squad, which goes to training camps at the Natl training center.
International elites have a higher qualifying score (and they do not have to test compulsories) and are trying to qualify to the US classic meet, and from there to USA Championships- where they try to place high enough to make the US National team. In order to qulaify international elite, you must get your 'score' at a designated National qualifier, or at the Natl training center.
Almost all athletes go through the above steps, but a coach can also submit a video to Marta Karolyi of their athlete, to try to get the athlete invited to a training camp.
TOPS is the step before HOPES, for athletes ages 7-11. The top athletes try to qualify to National testing, then try to qualify to the TOPs National Team. They attend a training camp if they make TOPs national team.
The usa gymnastics webpage (look on the TOPs page) has all the qualifying scores & information, as well as the compulsory routines.
Hope this helps.