This goes into General Discussion.
And I'll just break it down for you:
Imagine the numbers are directions (to get an good idea, look at your numpad to the right of your keyboard)
So 2 is down, 4 is back, 6 is right, 8 is up, and 5 is neutral, for example, creating things like 214A, 3C, 623C and 632146D. It's actually very simple once you get used to it.
A, B, C and D refer to the attack buttons.
JC is Jump Cancel.
JCC is Jump Cancel Cancel (canceling a JCable move in another move, like Black Onslaught.)
j.(A,B,C,D) refers to a move done in the air.
RC means Rapid Cancel.
IB is Instant Block.
And so on...
A simple to combo into Astral is 5C, 3C, 214741236C (Ultima says 21412369 might be a better option, but it's personal preference, really).