There are a couple things to look for to know what kind of hot water heater you currently have.
Gas – Is there a black or a flexible yellow or silver pipe going into the bottom of your hot water heater? If so you have a gas water heater. If there is a large PVC or Metal vent pipe coming from the top of your water heater you likely have a gas water heater. This vent pipe is used to force the exhaust created by the gas out of your home.
Electric – Electric heaters do not need the vent pipe from the top because there is no exhaust. If there is a large electrical wire (could look similar to an extension cord or small grey garden hose) going into the top of your heater this indicates you have an electric water heater.