Simple explanation of dative bonding
Alright, I will keep this extremely brief. You know the following things I presume:

Ionic bonding - formed when electrons are transferred from one atom to another, forming a cation and anion.

Covalent bonding - formed when two atoms share an electron pair

Dative covalent bonding - formed when two atoms share an electron pair, but this electron pair comes entirely from one of the atoms

For example, in a Hydrogen to Hydrogen covalent bond: 

H-H

They share a pair of electrons, one electron coming from each.

However,in the carbon monoxide molecule, there are two normal covalent bonds and one dative bond. In the dative bond, both electrons are initially from the oxygen, and are then shared between the two.



Hope this helps