The molecule of water is not a straight line of atoms. The two hydrogens are slightly to one side of the oxygen atoms (there are many great diagrams of this out there.)
Basically, the oxygen and hydrogens share electrons (covalently bonded), but since the oxygen atom is much bigger, it ha the electrons by it for more of the time. This causes the oxygen end of the atom to have a partial negative charge, and the hydrogen end to have a partial positive charge.
If there are two water molecules, they will tend to line up so that opposite charges are facing: oxygen side will tend toward the hydrogen side of another water molecule.
*Remember: opposite charges attract; similar charges repel*
This tendency forms what are called Hydrogen bonds, which give water its property of adhesion and cohesion, as well as surface tension.
Hope this helps! :)
