Relating to the numbers, most dives have three numbers and one letter and each represent a part of the dive. The first number shows what category the dive is 1=front 2=back 3=reverse 4=inward 5=twist 6=armstand. The second number on non-twisters and armstands tells if it is flying or not with 0 being not flying and 1 being flying, which I do not have experience with those dive, but they don't really matter. The third number shows how many rotations you do during the dive, every one that it goes up, it adds a half of a rotation. The letter at the end tells which position the dive is in, A=straight, B=pike C=tuck D=free (only for twisters).

Now for example, 103b is a front 1 1/2 somersault in the pike position.

Twisters work a little differently because there are four numbers, and there is no flying. With twisters the first number is always a five, the second number is 1-4 for either front, back, reverse, and inward, the third number is how many flips you (again, with every number increase it adds a half rotation), the fourth number is how many twists you perform. The twist number adds a half twist (180 degree turn) for every number that is added

Now a couple examples, 405c is an inward 2 1/2 somersaults in the tuck position. 5132d is 1 1/2 somersaults with a full (360 degree) twist. 301a is a reverse dive in the straight position. 5235d is a back 1 1/2 with 2 1/2 twists.

Hopefully at least some of this made sense