I have a well and the that comes from the faucets is a trickle. How do I refill the air tank to get the water pressure

You don't. The one thing to check on the tank is to find the little air valve at the top. Depress the valve stem. If water comes out, then the tank is waterlogged, but I don't think that is your problem. First thing to check is system pressure. Find your pressure gauge and tell us what it reads. Also, do you have a filter or water softener? If so, then try bypassing them.

Now you can certainly check the pressure in the tank. It should be set to 2# below the point at which the pump turns on. So if it turns on at 30#, then pressure in the tank would be set to 28#. This is done with the system off and pressure driained to zero by opening a low level faucet. But that does not fit the problem you are describing. The pressure tank does not created system pressure. The pump does that, so adding air to the tank does not increase pressure.

Either your pump is cutting off too soon, or there is an obstruction somewhere between your tank and your faucets.