I don't quite understand the question, either, but here is a very quick (and crude) primer on trunked radio:
When a user wants to make a group call, he presses his PTT. This causes a data word to be sent from his radio to the system controller, on the inbound side of the presently active control channel. If all conditions are met, the system controller makes a channel grant for the call, which takes the form of a data word on the outbound side of the control channel. This word advises all radios listening to the control channel that a channel grant for Talkgroup X has been set up on Voice Channel Y.
Meanwhile, our initiating user still has his finger on the PTT. His radio is still listening on the outbound side of the control channel and when it hears the channel grant, it switches to the assigned voice channel, issues a short word confirming that it has made the switch, and receives a response. At this point, his radio issues a series of beeps (the "talk permit tone") and User begins speaking.
All other users who are selected on the talkgroup but not scanning, or who are scanning but not listening to some other talkgoup at the time, hear the OSW and likewise shift and listen to the assigned voice channel. I suspect that any trunking scanner does exactly the same thing.
What happens if a non-initiating user is scanning and has stopped on some other talkgroup, and what happens when the initiating user unkeys are more complicated and saved for a more advanced course.