Large-scale structure formation in the universe is the final pillar in the Hot Big Bang Standard Model. We want to know how galaxy clusters formed, how dark matter came to be where it is. Also, we learn why galaxy clusters have so much hot gas, and how the absorption features in distant quasars came to be. We also see how the dark matter distribution can be mapped by its effect on galaxy's light and on the shape of clusters too. We also see how the Cosmic Microwave Background plays a central role in it all.