Hot wire cutting machines are tools that cut various foams like polystyrene or styrofoam with a heated wire. The wire is stretched vertically between the work plate and the boom and you can set the temperature according to the thickness and hardness of the foam block. The foam block is cut by slowly guiding it along the fence angle against the wire or moving the block free hand. A foot pedal turns the heat in the wire on and off. Please be careful to do not touch the wire while cutting to prevent burning your fingers. 
Hot wire cutting machines are traditionally used to create architectural models out of polystyrene, furthermore it`s an easy and fast method to create prototypes of objects in the very first steps of product prototyping to define size and shape. Other applications are to cast miniature worlds like dioramas or to cast shapes for fiberglass or carbon fibre coating processes. 
There are a lot of do-it-yourself tricks to create stencils (so called shape shifter) to cut complex, rounded or angled shapes, for more information about that search for „shape shifter wire foam cutter“ in your browser.