The three elements that are needed to start a fire are oxygen, heat and fuel. Those three elements are part of the fire triangle, which illustrates the interdependence of the ingredients that are necessary to start and sustain a fire.
A source of heat is required for the initial ignition of fire. It also helps sustain the fire and allows it to spread. Any kind of combustible material can serve as fuel. The moisture content of that material determines how easily the fuel burns. Oxygen supports the chemical processes that drive the fire, whereby fuel reacts with oxygen as it burns. This generates combustion products, such as embers and smoke, through a process called oxidation.