Apart from heat and fuel, which other component is essential to start a fire ?
Oxygen
To start a combustion process we need something to burn first of all, this substance is the fuel.
Combustion process is the oxidation of a fuel to give off energy, hence oxygen is necessary.
To actually start the burning process, a fuel has to be taken to its ignition temperature by the application of heat. The heat can be supplied in many ways, e.g. friction or another fire.