How do you wire up a hot water heater if the wires from the water heater are red and black and the wires from the wall are black and white?

Black to Black
White to Red

I agree with KISS but I would also verify that you have 240 coming from the white and black, this may be just a 120 line. Check with a meter, black and white should each show 120 and then you are good to go. If only the black shows 120 then the white could be the neutral of a 120 line.

10/2 cable is typical to feed an electric water heater in the US. This is black and white, along with the ground.
Most electric tank type water heaters have a black and a red in the wiring compartment.

With that said, see KISS's post.