In this paper we wanted to find out at which redshift the "first object" forms. The formation of the first structures in the Universe is driven by the gravitational collapse of small inflation induced matter density perturbations existing in the primordial matter density field. In CDM and BDM models of structure formation, the smallest objects are predicted to be the first ones to go nonlinear. It is expected that first non-linear objects in the Universe to form for dark matter halo masses at redshifts between 10 - 30. A crucial conditions for these DM halos to form stars or galaxies is the ability of their gas to cool in a Hubble time. Cooling is important in early Universe because it controls the collapse of the first objects. At high temperatures, primarily effective is atomic cooling which is dominated by hydrogen and helium. The most important for molecular cooling and the most abundant molecule is H2 . The first objects are the building block of the following structure formation and this leads to larger formations through accretion and mergers, such as galaxies and galaxy clusters . The epoch after formation of the first object is known as the epoch of reionization. For the formation of the first object we require to have enough energy to reionize everything. The reionization usually refers to the reionization of hydrogen since mostly baryonic matter in the Universe is in the form of hydrogen.