Polarity is the unbalanced distribution of charge in a molecule. It results in the molecule having a negatively charged and pisitively charged end. For something to be polar it must contain a polar bond, a bonds polarity is determined by the electronegativity of the two atoms in the bond. with respect to the Pauling scale a polar bond is when the difference in electronegativity is between 0.5 and 2.
Water is a polar molecule, the electronegativity of oxygen is greater than the elctronegativity of hydrogen therefore the two oxygen-hydrogen bonds are polar.