In water, a hydrogen bond can form between a hydrogen atom of one molecule and which atom of another molecule?
The hydrogen bonding in water is between one of the hydrogen atoms of one molecule and the oxygen atom of an adjacent water molecule.
Because water molecules have a bent shape (a bit like a banana) and because oxygen is more electronegative than hydrogen, the charge separates with the oxygen end of the molecule being slightly negative charged and each hydrogen being slightly positive charged. That charge separation can lead to attraction between these opposite charges. This attraction is described as hydrogen bonding.