1. Remove hydratn cap
2. Install the valve/gauge
3. Install hydrant wrench
4. Turn the wrench
5. Open the valve all the way. Hydrants have 2 openings, top and bottom. If you open the valve only part way, the opening on the botttom will wash out the hydrant. A hydrant that is washed out will sometimes have water coming out around the base of the hydrant. Keep washing out the hydrant will lead to a large hole in the dirt. The amount of water filling your tank is regulated by the gate valve or the ball valve at the outlet of the valve/gauge you screwed on the hydrant.
6. To shut down the valve, close the gate valve or ball valve. Remove the hose going to your tank. Close the hydrant, using the hydrant wrench. Just as the hydrant is closed, open the gate valve/ball valve. Put your hand over the outlet, continue to close the hydrant and you should feel the suction as the lower valve closes. the lower valve closes last so the water in the hydrant will drain and not stay in the hydrant and freeze. Remove the valve/gauge and look for water dripping out of the hydrant.
7. Install cap. Ask if they want you to use grease on the threads.
I am surprised you were not given a quick lesson in hydrant use. You must have a water purveyor, Fire Departments are very choosy on who they let use their hydrants. They want to make sure the hydrants are opened and closed properly.