The basic syntax of originate is as follows:

    originate <dialstring> <destination number>
  

It gets exactly the same dialtrings as the bridge application in dialplan. Actually, as "destination number" argument it accepts dialplan applications, so you can have this kind of command line:

originate sofia/internal/[email protected] &bridge(sofia/internal/[email protected]) 

This will originate a call to userA, and if userA answers, will originate an additional call to userB. If userB answers, it will bridge the two calls and the two users will be able to talk.