In addition to the mat you will also need the heating cable and a thermostat.
The mat can be cut to size, but the wire cannot be cut so you will need to select the appropriate size. When determining the floor area to be covered by the cable, make sure that you are allowing at least 6" of clearance to any walls or built in obstacles such as cabinets, showers, and toilets. Also, provide 10" of clearance to any heat sources such as fireplaces, baseboards, etc.