This process is best answered by the Flotilla Human Resources Officer, called the FSO -HR .
Essentially, you should discuss your interest in joining the Auxiliary. The FSO-HR should provide you with both an application and study materials. When you are ready you can setup an appointment to meet the FSO-HR and both take the New Member Test and complete the application and fingerprint process.
If you are joining one of several Auxiliary programs, you will also need to file a SF-86 , which is a US Government form used for a security background check. Again, your Flotilla FSO-HR is the best source of local information. As in the military, the Auxiliary uses a Chain of Command, but we call it a Chain of Leadership and Management, or COL. (you'll read about this in the study material).
So , all questions should be addressed at the local level and work it's way up to the top level, not visa versa.