The flamethrower was used by the Germans. The main point of the flamethrower was to burn anything. People, supplies, food, or buildings. But they were normally used for a fear factor. Once the enemy got over the fear of the sight of the fire, they would continue to fight as normal. There were two main types, the Kleinflammenwerfer and the GroBflammenwerfer.
The Kleinflammenwerfer is smaller and can be carried by a single person. Small units of flamethrowers were sent in groups of six or so to fight off the defenders and open the way for the attacking Germans. The Kleinflammaenwerfer uses pressurized air and either carbon dioxide or nitrogen to shoot burning oil as far as 18 meters. Another portable version had canisters of gas on the flamethrower's back and a hose with a lit nozzle on the end to ignite the gas. Two cylinder versions have propellant in one tank, and flammable liquid in the other. The fuel is shot through the tube and ignited at the end of the nozzle.The GroBflammenwerfer is larger and could shoot about 36 meters. It was could sustain flame for 40 seconds and needed more men to operate it.
The French and British developed their own flamethrowers, both designing ones better than the Germans. The British found that besides clearing trenches, the flamethrowers were pointless, so they stopped using them almost immediately. The French made one for trench attacks that the Germans used to base a new flamethrower off of.
"Two fellows with a flamethrower are seen, one carries the tin on his back, the other has the hose in his hands from whcih the fire spouts. If they get so near that they can reach us we are done for, we cannot retreat yet" (Remarque 283).
Being a flamethrower is very dangerous. Having a tank strapped to your back is not exactly going to make it any easier to run. If you run out of fuel, then you are stranded with no weapon, so flamethrowers had to be careful and not waste their fuel. Also, you are very visible, especially at night, making you a huge, glowing target. If flamethrowers were captured, they were rarely taken as prisoner and were more often killed.
Near the end of the war, flamethrowers were attached to tanks.