If you are not already on a call, then you can just dial the number.
The first available appearance button is automatically selected for the call.
The call uses either the phone's speaker or headset depending on the phone's default handsfree audio setting. To switch to the handset, just lift the handset.
If the number you dial matches a user or group on the telephone system, the directory name is shown and the call starts altering them. Otherwise, as soon as there are enough digits the phone will be connected to an external telephone line.
If the call is to an internal 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.