Sink
In order to use your sink, simply open the tap to have access to water on your sink.
The California is equipped with a 50L clean water tank and 40L waste water tank underneath the van.
Stove
In order to use the stove you have to turn on the gas tank by flipping the lever underneath your kitchenette so the gas can travel to your stove. After cooking to be on the safe side please always turn off the gas lever.
You can start the stove by turning the black wheel and pressing the button (or use matches provided inside the kitchen cupboard)
Other relevant articles:
How to change the gas bottle