🔖 In this work, first chapter contains some important definitions and some fixed point theorems which are used to prove our results. Second chapter is devoted to the study of existence of coupled solution of an equation. In third chapter the existence theorem of coupled coincidence point is proved. In fourth chapter the existence of mild solution of initial value problem for nonlinear equation with nonlocal initial conditions is obtained. In fifth chapter, we discuss the asymptotic behavior and the existence of periodic solution of first order nonlinear difference equations.Sixth chapter is devoted to the study of existence of solution of a summation equation. In the last chapter, the unique common fixed point for two pairs of weakly compatible mapping is obtained.