You will go to your nearest ASTC unit and take physiology training. It consisted (for me) of a few hours of classroom instruction on different physiology topics, a little bit of hands-on experience with survival gear, a ride in the hypobaric chamber (only to 8k ft for mids), a brief swim using survival strokes both in and out of flight gear, a simulated underwater egress (not in the dilbert or helo dunker for me), a parachute harness drop into the pool, and finally a dynamic seat ride if you are planning on going to a squadron that flies ejection seat equipped a/c. Its not a big deal and can be done in a single day if need be (though normally 2 days I hear). I had mine done about 2 weeks prior to leaving for Lemoore on my 1/c cruise. Don't stress about it....even the most incompetent swimmers eventually pass unless they REALLY don't want to. Hope that helps