The notion of what constitutes matter in fact is not static but evolves with time, changing in step with technological advances or more precisely with the growth in the power of the sources of energy that become available to the experimenter. It is successively discovered that matter is build up from molecules; that the molecules are composed of atoms; the atoms of electron and nuclei; and the nuclei of protons and neutrons. Extensive researches, since the start of nineteenth century, have been carried out by the scientists to conclude about the ultimate representatives of the matter, i.e. the basic building blocks called the elementary particles or sub-atomic particles. The book devotes mainly to the higher order effects in structure functions and some aspects of high density quantum chromodynamics. The analysis is based on Dokshitzer, Gribov, Lipatov, Altarelli, Parisi (DGLAP) evolution equations which are the basic tools to study the underlying dynamics of quarks and gluons.