In one sentence, describe what the following article is about:

A tool should have come with your oxygen tank that can fit over the top valve on the gas tank itself. Position the wrench over the valve and turn it counter clockwise to open up the airflow from the tank to the regulator. When you unscrew the valve on the top of the tank, you should see the needle move, signifying that there's air coming through your tank. You should also hear and feel oxygen coming through the tube that you connected to the regulator. Your doctor should have informed you of the number that you should keep your regulator at. Follow their instructions and adjust the level of oxygen by turning the dial on the side of the regulator up or down. On the dial, you should see numbers. Move the dial until the number lines up with what your doctor told you. Never change the level of oxygen unless instructed by your doctor. The cannula is the small tubing that fits inside of both your nostrils. Put the parts where the air is coming out into your nose and stick the rest of the tubing up and over your ears. This will keep it in place as you walk around. Sometimes your oxygen tank will come with a full oxygen mask. If you have a facemask, place the mask over your mouth and nose and put the straps on the mask behind your ears. Using the same cannula for over a month will make you more prone to infections. For the same reason, you should also change your cannula after you've been sick. Your tubing will also need to be replaced every 3-6 months. Turn the valve clockwise on the top of your tank to turn off the airflow. This will prevent you from wasting oxygen whenever the tank isn't in use. Consult with your doctor to determine how often you should be using it and when you should turn it off.

Summary:
Unscrew the top valve one full turn. Watch the needle on the gauge go up. Adjust the level of oxygen coming through the tank. Insert the prongs on your cannula into your nostrils. Replace your nasal cannula every 2-4 weeks. Turn the tank off when you're not using it.