Percolation theory describes a phase transition process. There is a natural parameter which describes sudden change in the behavior of the system. Such natural parameter in percolation theory is called critical probability. There are two stages of the percolation process that are determined by the value of critical probability \(p_c\) and the probability p of a fixed edge being open. When the probability p is less than the critical probability \(p_c\) then the process is called the subcritical phase, otherwise it is known as supercritical phase. Open infinite cluster does not exist in the subcritical phase while in the supercritical phase it exists. If the probability for the existance of an infinite open cluster is strictly positive then there is almost certainly unique. From the basic process of the percolation theory we can develop much more complex processes, and thus significantly expand the range of their application in biology, physics, chemistry and astronomy.