It varies by jurisdiction (state, federal, city, etc).
The last time I looked at one state ... it was HB for House Bill, or S for Senate ... and the number was sequential, and reset each session. So the first House Bill was HB-1. Of course, a lot of them never make it to the floor or out of committee, so the public may not hear of one until (say) HB-507 is up for debate.
Statutes are by Title, Chapter, Section, Subsection. It's pretty self explanatory. The others are different in the many many jurisdictions and could be simply chronological, numerical, a mixture, or something unique to the jurisdiction.