van der Waals forces are weak attractions that occur between molecules or parts of molecules. These forces arise from temporary shifts in electron density, leading to slight positive and negative charges. They play a crucial role in various physical properties, such as boiling and melting points. There are three main types of van der Waals forces: London dispersion forces, which occur in all molecules; dipole-dipole interactions, which happen between polar molecules; and dipole-induced dipole interactions, where a polar molecule induces a dipole in a nonpolar molecule. Together, these forces influence molecular behavior and interactions.