Some examples are:
#1s_A + 1s_B = sigma_"1s"#
#1s_A - 1s_B = sigma_"1s"^"*"#
#2p_x + 2p_x = pi_"2px"#
#2p_x - 2p_x = pi_"2px"^"*"#
#2p_z + 2p_z = sigma_"2pz"#
#2p_z - 2p_z = sigma_"2pz"^"*"#
where #+# implies orbital overlap in-phase and #-# implies orbital overlap out-of-phase, and the #2pz# atomic orbitals overlap colinearly while the #2px,y# orbitals overlap parallel. The asterisk simply distinguishes whether one of the molecular orbitals is bonding or antibonding. The bonding orbital has no asterisk.
When these orbital overlaps happen, a bond is made, so you either get a new #sigma# bond or a new #pi# bond like the ones above (except they are just called #sigma# bonds or #pi# bonds, without the #ns# and #npx,y,z#).
