Abstract: Active matter is a typical non-equilibrium system, which has become an important developing field in soft condensed matter physics. It is composed of micro-driven particles, where driving forces are applied on every particle independently. In this introductory article, we give a brief account of some specific active matter systems, where interesting phenomena are observed or predicted. We describe the structure, behavior and special dynamics of various active states, such as active liquid-gas, ferromagnetic, nematic, and gel states.