I'll preface this with "I'm a cutter guy," but a good majority of my Academy friends have gone into Aviation (more's the pity).
You first have to elect between fixed wing and rotary. The amount of people per class that is able to go into each field is determined by current service needs. There are some classes where there is only one or two fixed wing slots or none at all. Once you have selected or been assigned fixed or rotary, you will then continue onto more advanced courses of study for that airframe, and then closer to your winging date you will select your specific airframe.
Then the progression gets a little fuzzier to me, but eventually you report to your first duty station and then go to T Course.
... by which time if you went straight from the Academy, your classmates are already halfway through their second operational tour afloat.