What’s does A1 and A2 mean and/or B1 and B2 mean?

This just means you couple those exercises together, or what we call a superset. Basically, you go from the A1 exercise and then immediately to the A2 exercise without rest and perform the second exercise then rest the allotted time.

Some instances these supersets can go longer than 2 exercises they can look like this A1, A2, A3, etc. All this means is you go to each exercise in the series without rest and rest at the end of the series.