How to turn off a water heater?

First, disconnect energy supply, IE. Electric breaker, Gas valve.

Locate drain valve at bottom of water heater, connect garden hose to valve.

Run water hose to drain adequate to accept a lot of water at once, must be lower than drain valve on water heater or if it's not an issue where you live simply run hose to somewhere outside where hot water isn't going to cause a problem (watch flower beds, children, pets getting too close etc. Weight the end of the hose so it doesn't flop around uncontrolled.

Now just leave the water valve turned ON and ope the drain valve. Water will enter the top ,exit the bottom. This is a flush. If you have hard water with no water filters and your water heater's quite old this might not be accomplishing much.