Hydrogen bonding occurs in molecules when a

When an hydrogen combine with another hydrogen example in the case of water

The answer is: hydrogen atom bonded to small electronegative atom is attracted an electron pair on an electronegative atom on an adjacent molecule

The bonding would make the molecules become stronger even though it might not be as strong as a covalent/ionic bond. The attract The attraction could be considered as a dipole dipole attraction, meaning that it happen between positive and negative ends of polar molecules.