BF3 is a nonpolar molecule. While it does contain three nonpolar bonds, which are all between the central boron atom and the individual fluorine atoms, the symmetrical molecule shape results in a nonpolar molecule.
Bonds are formed between atoms when electrons are shared or transferred. In the case of a covalent bond, which typically occurs between two nonmetal atoms, the atoms share one or more electrons. If one atom has a stronger electronegativity than the other atom, it will exert a greater pull on the electron and attract it slightly closer. This creates a dipole, which consists of a slight negative charge on the stronger atom, and a slight positive charge on the other atom.