In polar molecule there is a uneven distribution of charge which results into positive and negative pole in the molecule. For example in water molecule, oxygen has negative pole due to the two lone pair of electrons on it.
In a non-polar molecule is the electrons are distributed more symmetrically and hence does not have an abundance of charges at the opposite sides. The charges all cancel out each other.For example in carbon dioxide which is symmetrical hence has even distribution of electrons and is non-polar.
Electronegativity is the tendency of an atom or radical to attract electrons in the formation of an ionic bond.