We study the formation of first bound objects in the Universe after recombination. We trace the evolution of a spherically symmetric density perturbation in the \Omega =1 Cold Dark Matter (CDM) model with baryon and dark matter contributions, respectively, \Omega _b=0.1 and \Omega _dm=0.9. Physical processes in the collapsing gas relevant to various stages of the nonlinear collapse of low mass objects are considered. We find that the first density perturbations which collapse to form luminous objects have baryon mass in the range 10³--10⁴ M_\odot . The final collapse of these objects is triggered by the cooling due to H₂ molecules and it starts early at redshifts z \sim 20. The role of the initial baryon overdensity in the collapse of density perturbations in CDM model is studied.

PACS numbers: 95.30.Lz, 95.35.+d, 98.35.Mp, 98.80.Bp