First, program the control channels of the systems you want to monitor. They are listed in red on the TRS page of interest. Program these in the appropriate trunked mode (MO or ED).
Then trunk the bank. Press Program+Trunk, and press mode until the appropriate mode is selected.
Then enter the talkgroup values of the groups of interest in the appropriate memory slots.
Put the bank in Open Mode to hear all talkgroups active on the system, or in closed mode to only hear those you have programmed.
This is all explained in detail in the scanner's owner's manual and on the rr wiki. If you don't understand it, read it again - it's all there. If you get stuckon something, ask a specific question.
Also consider using programming software (Win97 from StarrSoft is recommended). This will help you understand the memory configuration of the scanner.