What are 3 major parts of a bow?

A long bow is basically one stick of wood (ash, yew, or witch hazel during the hundred year war).

If you look into it's technical parts and divided it visually without physically taking it apart, then it would consist of a grip, a main piece (called a riser in modern terms), two limbs on either side, and (once ready to use) a string.

Hope that answered your question. Look back into the Hundred Year War for England and see their longbow usage for more information.