Na⁺ is a cation, that is, an ion with a positive charge.
NH₃ has polar covalent bonds (due to the difference in electronegativity between nitrogen and hydrogen). According to the VESPR theory, it has a trigonal pyramidal shape with a lone pair. As a consequence, it has a net dipole moment and the molecule is polar.
The intermolecular forces between Na⁺ (ion) and NH₃ (dipole) are ion-dipole forces.
