In order to access the Forwarding setting, click on the "Forwarding" tab (as shown in the picture below)
These are what the options within the Forwarding tab will do:-
Forwarding Unconditioning - Enabling this will forward all calls to a number set by the user
Forward Number - This is where the user will set the number they want calls to be forwarded to
Forward On No Answer - Enabling this will only forward calls that have not been answered
Forward on Busy - Enabling this will forward all calls if the user is busy (already using the phone)
Forward to Number when Phone is busy or call is not answered - set number to forward to when Phone is busy or call is unable to be answered