Trees are cut down (deforestation) for many reasons including
forest pointTo be used, sold or exported as timber, wood or fuel (charcoal). This is called logging.
forest pointTo be used for farming purposes (grazing fields for livestock, or large scale farming activities)
forest pointTo make room for human settlement and urbanization (these include making space for shelter, industries and roads)
forest pointTo make room for mining. (More on deforestation here)