If you are not already on a call, then you can just dial the number. The first available appearance button will be used for the call. Alternatively, you can press a specific appearance button in order to make a call using that button.

If the number you dial matches a user or group on the telephone system, the directory name of the user or group is shown and the call starts altering the target.

If the call is to a user, and they do not answer, you can set a callback by pressing CallBack and then ending the call by pressing Drop. When a callback is set,  the next time a user uses their phone or ends their current call, the system will call you and when you answer, automatically make another call to the user.