What makes a molecule polar?

Two questions to ask

Are any bonds polar? Atoms with different electronegativities pull shared electrons unequally. Do those bond dipoles cancel? A bent or otherwise asymmetric arrangement often leaves a net dipole.

Water is a useful example: oxygen pulls electron density through two O–H bonds, and the bent H₂O structure prevents those bond dipoles from canceling. A straight line alone is not proof of nonpolarity: HCl is polar because its two atoms are different.