[soperj]

Can you explain what the difference between /4 and /8 are? like for example, what is the difference between 9/8 and 9/4? I've made something up that has an 11 time signature, 2-3-3-3(or 3-3-2-3), but how do I know if it's 11/8 or 11/4?

[x3n0ph3n3]

It only indicates which note symbol is the beat unit. /4 means that each quarter note gets the beat, while /8 means that each eighth note gets the beat. 3/4 means there are 3 quarter notes of time, while 6/8 means there are 6 eighth notes of time. This might help: https://en.wikipedia.org/wiki/Note_value

[bonzini]

You don't. However, in general faster tempo has a lower denominator (in classical music at least, and more rarely in jazz).

For example, a 2/2 tempo with 100 BPM is easier to "manage" than a 4/4 tempo with 200 BPM, and they are the same as each 2/2 beat corresponds to two 4/4 beats. So a "Presto" or "Prestissimo" will often be written as 2/2, with half the BPM that it would have in 4/4. Likewise, a 6/4 is usually faster than a 6/8 or 12/8.