What type of fuel is used in helicopters?
It depends on the engine. A piston engine will use avgas (aviation gasoline) or diesel (or Jet-A for availability reasons) depending on whether the engine is a diesel engine (which can burn jet fuel), while a turbine engine will use jet fuel. Essentially whatever the engine is rated to burn.

The fuel tank is somewhere in the fuselage near the center of the rotor. This to avoid the center of gravity shifting with the fuel level.