Why are anti$-$bonding and bonding formed in a molecule what is the reason need, does it happen naturally?

what is an antibonding and bonding when two molecules meet and do they occupy the lower energy bond because of its lower energy and we know that the systems in the universe tend to go towards lower energy is that the reason

And is this the reason conduction band are empty IN a lattice and valence band filled,?

Is it the shell of atoms that bond or orbitals like s$,$p$,$d etc

What Is wave function? Is it about the location $($ probability$)$ of the electron etc?$($ YES OR NO$)$ If so what is its use?