Look at the backside of water heater (from inside the RV)
Need to OPEN cold water inlet to WH Tank (bottom valve)
Need to CLOSE 'bypass valve' (on line that connects cold inlet with hot outlet)
Hot outlet....might have a valve that needs to be OPEN but more likely no shutoff valve but a check valve that will OPEN when water flows out of WH Tank
Water Heater Tank will take a while to fill ----6 gal/10 gal
Post BRAND/MODEL of water heater for SPECIFIC info
On Edit: Looking at photos you have an Atwood
S/B a dual on/off switch with RED light between switches
Left side for electric element (need 120V AC Power and 12V DC)
Right side for propane (need propane AND 12V DC)
12V DC used for control power for both electric and propane
Electric element and DC Relay on backside of WH Tank
Propane is DSI (electronic spark)
T-stat is pre-set to OPEN at 140*F and CLOSES at 110*F (to heat/reheat water)
ECO (Energy Cut Off/HI temp t-stat) OPENS at 180*F and triggers RED FAULT Light on switch panel
*ECO will CLOSE when water temp drops below 150*F BUT FAULT Light/Control circuit has to be reset by turning switch OFF--wait 30 seconds--turn back ON
If propane fails to light off and prove it lit....circuit board makes 3 attempts then 'locks out'----triggers RED Fault Light (same reset procedure)
**common issue when FIRST using RV after propane has been valved out