Galaxy clusters form through merging and accretion of smaller structures along large-scale filaments. During merging events, the state of the X-ray emitting gas is perturbed, which is at the origin of the classification of clusters from their X-ray properties into cool-core and non-cool core systems. I will present the analysis of X-ray selected cluster samples, with the aim of measuring the fraction of cool-core clusters in the present Universe, which can be used to estimate the merger rate. I will also focus on the accretion processes at work in the outer regions of galaxy clusters.