n chemistry, hybridisation (or hybridization) is the concept of mixing atomic orbitals into new hybrid orbitals (with different energies, shapes, etc., than the component atomic orbitals) suitable for the pairing of electrons to form chemical bonds in valence bond theory. Hybrid orbitals are very useful in the explanation of molecular geometry and atomic bonding properties. Although sometimes taught together with the valence shell electron-pair repulsion (VSEPR) theory, valence bond and hybridisation are in fact not related to the VSEPR mode
Hybridization is a process which involves intermixing of orbitals of comparative energy, redistribution of energy and leading to formation of hybrid orbitals having same shape and energy. s and p orbital also undergo hybridization
One s + one p = two sp hybrid orbitals 
One s + two p orbital = three sp2 hybrid orbital
One s + three p orbital = four sp3 hybrid orbital.