The difference between search and scan is about the same as the difference, in a conventional (non-trunked) scanner between searching a range of frequencies or scanning a list of frequencies. If you know the talkgroups you want to hear, use scan. If you want to see which talkgroups are active on the system, use search. The scanner will still "give you" the first talkgroup it sees, whether that's one you programmed in (scan) or the first one to use the system (search).