Can someone tell me how to test the voltage coming from a circuit breaker?

Preferably in a way that doesn't involve killing myself. I installed a new hot water heater today because the old one seemed totally dead. Well, the new one doesn't work either. I know there is power coming from the wires because I used one of those little LED outlet testers on the leads and got a light. However, I wonder if its not enough to juice to run the water heater or if something has trashed the power coming from the circuit breaker. I have a multi-meter, but I have no idea what to set it for. Anyone who knows what to do and could maybe reference a website with instructions, that would be great! Before I drop hundreds and hundreds of dollars on an electrician, I would like to make sure the power is really the problem and I wasn't just unfortunate enough to get a DOA water heater.