So you have a molecule which is full of electrons, and at any moment in time these electrons can move to one side of the molecule. As we know electrons are negatively charged, if they suddenly move to one part then this will cause a charge difference. This is called a temporary dipole! This will induce another charge difference (a dipole) in the molecule next to it, which will then go on to induce another dipole in its neighbouring molecule in a domino effect and so on. The dipole means that part of the molecule is slightly negatively charged and the other part is slightly positive. Because we know opposites attract, there will be an attraction between the slightly positive part on one molecule and the slightly negative part on another molecule.