sandpiper 5th wheel

First, your posted in the wrong forum. Did ask the mod to move it for you.
I assume your asking about a Suburban water heater? Which model?
The small rocker switch down low on the left side is indeed the 120V off on switch for the electric element. However that switch is very prone to failure and often is stuck in one position. Personally I never use it, leaving it in the on position. Instead, I turn off the 120V breaker

Everything he ^^^ said plus Make darn sure the water heater has water in it before you flip that little switch to ON. If the element is good, in about 30 min you should start to notice the water is getting warm. If not, it's diagnostic time.