Welcome to Radio Reference!
We could better help you if we knew your location, what type of system you are trying to monitor, and the specifics on what you have programmed in.
Since you mention talk groups, I am assuming it is a trunked system (probably Motorola Type II). If that is the case, be sure you have the bank set to MO, program in the control channels, and set each channel to MO. At that point you should hear all traffic on the system. In order to hear only certain talk groups, you would need to program those in (PGM, Trunk) and set the bank to Closed Mode (FUNC, period key).
I’m not sure I’ve answered your question, but I hope this helps. If not, please give us more specifics on exactly which system you want to hear so that we can help you get going!