Look near your water hookups for a water heater bypass switch. Make sure the switch is not in the bypass position. Connect city water hose and turn on water. Open a hot water faucet inside and wait until it blows all the air out and water starts flowing. Should take a few minutes to fill the water heater and water to reach the faucet.
Once you have water, then look for your water heater control switches, one for electric and one for propane.
If you have a Suburban water heater there will probably be a small black rocker switch on the lower left front panel of the water heater itself that also must be turned on for electric. You will have to remove the outside grill covering the water heater to access that switch. Then you can turn on the inside electric switch. And the water should start heating.
To operate on propane you need to have a propane tank valve opened and air purged from the propane lines. You can do that by turning on a stove burner valve until you can get the stove burner to light and then turn it off. Then you should be able to turn on the water heater propane switch and get the water heater to fire up on propane.
If there is no water heater bypass switch, then there may be valves behind the water heater that must be positioned properly. Then you would need someone knowledgeable to do that as there are several variations of that.