I don't think there is a pilot light any more. They all have automatic ignition. All you should have to do is turn on the switch, either gas or electric. Just make sure the water heater has water in it.
How do I light it? Book says its auto but the control panel says it out.
When you activate the switch, you'll see it light up momentarily, then go out. That means its working! If the burner will NOT fire, the light will stay on. At least that's the way my Suburban HW heater works. Yours may be different. If in doubt, turn it on then go outside and listen to see if it's working.
Probably depends on your heater. For Atwood heaters at least, there is a different part number for a piezo starter than one for a pilot light. Find your heater part number (it should be behind the heater's access door on the outside of the RV), then search the internet for a manual - just about everything is on-line these days. Also, there are usually several YouTube videos on how to do things like this.