I gave a talk at the UM HET journal club on the Extended Press-Schechter formalism, which describes the number density distribution of halos (galaxy clusters) in ΛCDM. It starts from basic cosmology but assumes some results from inflationary theory without demonstration. The Press-Schechter formalism was a mildly accurate formalism with some problems; these problems are resolved in the extended formalism. Thanks to Dragan Huterer, my cosmology professor, for notes and to the very clear textbook MBW. You can access the lecture notes here.