I accidentally hit the valve release with my arm. No it won't stop dripping. I did not open it to where I had to close the valve. How can I get it to stop?

You will need to replace the valve.
They just screw out. And are available at any hardware store.

To replace, just shut down the power, cut off the water supply.

Remove the old valve, wrap the new valve threads in some telfon tape, or pipe dope, and screw in in, tighten.

Open a hot water fixture, and turn on water supply, allow tank to fill (will be evident when water comes from the fixture)

Shut off the fixture and inspect the valve for leaks.

Turn water heater breaker back on (resupply power)

Enjoy!

Are you talking about the water heater T&P valve or some other pressure relef valve.

If it is the T&P valve I agree with andrew to replace it, but some time a little dirt gets stuck inside the T&P you can do this before replacing it, close the cold water shut off valve drain some water from the water heater open the T&P valve and open the cold shut off valve let the T&P drain a little water close it and see if it will stop leaking then you will be OK if not you need to replace it as andrew says see the image below, Thanks.

John