  We will discuss here how structures observed in clusters of galaxies can
provide us insight on the formation and evolution of these objects. We will
focus primarily on X-ray observations and results from hydrodynamical $N$-body
simulations. This paper is based on a talk given at the School of Cosmology
Jose Plinio Baptista -- `Cosmological perturbations and Structure Formation' in
Ubu/ES, Brazil.
