We offer gentle introduction to Khovanov homology. We start from chain complexes and classical examples of homology (for simplicial complexes, groups and quandles). We introduce the notion of (pre)simplicial sets (and modules) and (pre)cubic sets (and modules). We show how to construct geometric realization of (pre)simplicial and (pre)cubic sets. We give an elementary definition of Khovanov homology of links and discuss geometric realization in extreme and almost extreme grading.