Those work the same as a regular 2500 analog phone. If they're pretty much the same as the 6221 that we use, it should have a 'flash' button that flashes the switchhook.
To transfer a call, hit the 'flash' button and the user should hear a dial tone. They dial the number they want to send the call to, then hit the flash hook again and hang up. If they don't hang up, it becomes a 3-way conference call.
I don't think you can program those buttons above the dialpad for commands in the same way as for digital phones. They are simple 'speed dial' assignments that are local to the phone. The lowest button on the left is usually the 'program' button.