Exactly how will depend on what type of trunked system you are trying to program and which brand/model scanner you are using. But basically it boils down to setting up the system by indicating which type of system it is, programming the control channels, and THEN entering the talkgroup IDs. Here is a link that will hopefully have your particular scanner’s manual in an easier to read form.
Mark's Scanners
There are forums for the different brands of scanners (Uniden, Radio Shack, GRE) where you might want to ask specific programming questions. A lot of people use software to help save time in programming, and with a premium membership here at Radio Reference, you can very easily import systems and be up and running in no time. I haven't yet learned how to do this, but others can help you get started. Good luck and hope this helps.