In an ionic bond the atoms are bound together by the attraction between oppositely-charged ions for example sodium and chloride form an ionic bond
In a covalent bonds the atoms are bound by shared electrons in a true covalent bond the electronegativity values are the same, although in practice the electronegativity values just need to be close if the electron is shared equally between atoms forming a covalent bond then the bond is said to be nonpolar. Usually an electron is more attracted to one atom than to the other forming a polar covalent bond. For example the atoms in the water H2O are held together by polar covalent bonds.