Use of GE at an airport only requires your fingerprints and is active as soon as you are approved. In fact, your approval letter tells you such but is so poorly worded to be confusing (emphasis added):
We are pleased to inform you that your U. S. Customs and Border Protection (CBP), Global Entry program membership has been approved. You may use the program as soon as you receive and activate your new Global Entry card.
If you enrolled in Global Entry, you may begin using the kiosk immediately. Global Entry cards are only issued to Global Entry members who are U.S. citizens, Lawful Permanent Residents or Mexican Nationals (who are not current SENTRI members). Global Entry cards are not valid at the Global Entry kiosks.
I think the "cards are not valid at kiosks" should be changed to "cards are not
necessary to use kiosks."