Cant for the life of me figure out how to fill water tank?

The tank flush port is right beside the port I'm using. So I'm good on not mixing the two up.. Ive have searched and searched online and cant find any useful manuals. I have had the faucet open and water running to no avail.. Unless maybe I didn't have it open long enough. I would assume I could hear something running, (air, water pump) something but cant