The AAU website explains the dive groups, but doesn't explain what counts for them (is a tuck jump a dive?)
OK- as simply as I can
Firstly shapes:
A- straight
B- pike
C- tuck
D- "free". so usually for twists where you may twist straight but somersault tuck/pike.
Dive numbers:
First number is direction:
1- Forward
2- Back
3- Reverse (so "gainer" in gym terms, forward take off but back somersault)
4- Inward (back tack off, forward rotation)
5- twist
6- handstand
Next is usually 0. This number is ignored- harks back to the days when they did the "swan dive" type dives so is no longer needed.
Then it's number of half somersaults.
0- jump
1-dive from feet to head.
2- single somersault
3- 1.5 somersault
4- double somersault......etc.
So there you pretty much have the basics and you can put dive numbers together:
100c= tuck jump
101c= tuck dive
103c= 1.5 somersault in tuck
405b- inward 2.5 somersaults pike.
Some novice dives "line ups" can be slightly different- 10B is a pike fall- where they stand on the board in pike and fall in to practice entry.
Then it can get complicated as you increase difficulty
5132 for example: 5, so it's a twisting dive. 1, take off is forward, 3, so 1.5 somersaults, and 2, full twist. forward full twist, 1.5 somersaults.
Clear as mud? It's a relatively straightforward system. Everything will "count" and has a set DD.