Van der Waals forces are the sum of all electronic interactions between molecules that are not ionically or covalently bonded to each other. Physically these forces arise from variations in the electron density around a molecule. Due to the different atoms, a molecule may have a permanent dipole where one end has a higher electron density than the other, or an induced dipole, which arises from random motion of the electrons in larger, longer molecules. If two molecules have dipoles, the result will be an attraction, where the high density of electrons of one molecule (partially negatively charged) is attracted to the low electron density area of a second molecule (partial positive charge) and vice versa. These intermolecular forces are incredibly important in chemistry as they determine many physical properties of a substance (boiling point, vapor pressure, freezing point, viscosity, etc.)

Van der Waal's forces are charge fluctuations on otherwise non polar molecules. These charge fluctuations temporarily make the molecules polar, allowing them to interact electrically.