What is the general mechanism of covalent interaction?

The general mechanism of covalent interaction involves the sharing of electron pairs between atoms to form covalent bonds. 

Chemical bonds are typically formed when atoms either donate or share electrons. Covalent bonds are a type of chemical bond that are formed when atoms share electrons. When atoms that have unpaired electrons approach each other, they share their outer electrons to achieve a more stable configuration for the participating atoms. This satisfies the octet rule, which states that elements will strive to get a total of eight valence electrons - by sharing, gaining, or losing electrons - to become more stable. For covalent bonds, two atoms share a pair of electrons. 

A single covalent bond is formed when each atom shares one electron to form the bond. Hydrogen is an example of a single covalent bond. 

A double covalent bond is formed when two electrons are shared from each atom. Carbon dioxide is an example of a molecule with double covalent bonds.