Not too sure what you're asking, but essentially for the USAF & Navy you need to obtain an officer's commission (Academy, ROTC, OTS/OCS, etc.) and get selected for pilot training (various screening accomplished). At some point during your initial pilot training (about 5 months) you'll get "tracked" (fighter/bombers, transports, helos). The next 6 months are further training in the track (possibly at a different base). Towards the end of that training, you get your specific aircraft assigned. The next 3 -12 months are spent training in that aircraft.

The Army is a little different, so I'll let someone else tell you about that route.