Starting my very first FF6 hack and had some basic questions.

How does 00 00 31 translate to FB/0000?

When working with events, all calls are relative to CA/0000.

CA + 31 = FB

If you're trying to call FB/47D3 (for example), you'd have to write the destination address in little endian (reverse order, basically). So that instruction would look like:

B2 D3 47 31

B2 is the instruction to call an event, and the rest is the destination. Reading it in reverse:

31 47 D3

Relative to bank CA:

(31 + CA) 47 D3

FB 47 D3