Star clusters are stellar systems composed of a number of stars bound by the self gravity. Star clusters have been simply assumed to be coeval and share the same chemical composition among the stars. However, over the last few decades, observations have revealed that stellar populations inside clusters are not-so-simple. This complexity of stellar populations in star clusters can come from either the internal processes (e.g. stellar encounters, binary evolution, multiple star formation) or the external processes (e.g. cluster mergers). In my talk I will present a series of works based on the numerical simulations on the multiple stellar populations in globular clusters. I will, in particular, focus on the binary dynamics among the different generation stars and the comparison with the recent observations. In the second half of my talk, I will introduce several applications how to interpret the very recent observations of star clusters using numerical simulations.