Abstract: An optical lattice is an artificial light crystal which is formed by the periodic potential wells created by the interference of counter-propagating laser beams. Its periodicity and well depth can be accurately tuned by changing the power and frequency of the laser beams. As a clean, controllable experimental platform, the optical lattice has gradually became one of the most convenient tools used to simulate many-body systems. This article is a brief introduction tocold atom physics, with particular emphasis on Bose-Einstein condensates, laser cooling, optical lattices,and quantum transitions.