Suppose you want to view the atoms in ``A'' which are in contact with ``B''. Use the within <distance> of <selection> selection command. For purposes of demonstration, let A be protein, B be nucleic, and define contact as an atom in A which is within 2 Å of an atom in B. Then the selection command is
protein within 2 of nucleic
If you want to see all the residues of A which have at least one atom in contact with B, use
same residue as (protein within 2 of nucleic)