How do hydrogen bonds make water a liquid?

Hydrogen bonds are weaker than covalent bonds, in liquid water they form, break, and reform easily. Thus, the exact number of hydrogen bonds per molecule varies. Molecules of pure substances are attracted to themselves and this sticking together of like substances is called cohesion, thus make water a liquid.

More specifically, hydrogen bonds are an attraction between the electronegative oxygen and the less electronegative hydrogen on a different molecule. It is extra strong as far as intermolecular forces go because the oxygen bonded to the hydrogens pulls the electrons away from the hydrogen, leaving the positive nucleus more exposed.