What do you mean by bonding molecular orbital and anti-bonding molecular orbital?

Bonding Molecular Orbital:
Bonding molecular orbital is formed by the addition of overlapping of atomic orbitals. The wave function of the bonding MO may be written as:

Ψ (MO) = ΨA + ΨB.

Atomic orbitals having same sign forms the Bonding molecular orbital when the lobes of them combines. The electron density is greater in the region between the two nuclei of bonded atoms. The forces in this orbital tend to bring the two nuclei of the atoms together. Therefore, electrons in the bonding MO contribute to attraction between the two atoms. It has lower energy than the isolated atomic orbitals.

Anti-Bonding Molecular Orbital:
Anti-bonding molecular orbital is formed by the subtraction of overlapping of atomic orbitals. The wave function for the anti-bonding MO may be written as:

Ψ (MO) = ΨA – ΨB.

Atomic orbitals having opposite sign forms the Bonding molecular orbital when the lobes of them combines. The electron density is lesser in the region between the two nuclei of the atoms. The forces in this orbital push the nuclei apart. Therefore, the electrons in anti bonding MO contribute to repulsion between the atoms. It has higher energy than the isolated atomic orbitals.