A covalent bond is formed by sharing of electron pairs between the atoms.
For many molecules, the sharing of electrons allows each atom to attain the equivalent of a full outer shell, corresponding to a stable electronic configuration.
There are mainly two types of covalent bonds (1) sigma bond (σ) and (2) pi bond (π).
A sigma bond is formed when one electron is shared from each atoms. Example: H2, CH4 etc.
A pi bond is formed when more than one electrons are shared from each atoms. Example: N2, C2H2, C2H4 etc.