There are several ways to create the reinforcement for a slab.
1. create a reinforcement drawing of the slab (you will get different views to formwork) and add the rebar elements into this drawing
2. assign a rinforcement style to the slab and create the reinforcement drawing.
Advance creates the rebar elements in this case automatically.
After the reinforcement is created in the drawing you can use the button "create a list..." to create BBS.
Or you type the command "grtclist" in the command line