In 1999 Khovanov introduced homology groups for classical links such that coefficients of the Jones polynomial appear as alternating sums of the ranks of these groups. In the talk, down to earth adaptation of this construction will be discussed. It is generalized to a class of virtual links (or abstract Gauss diagrams). The original chain complex defining the Khovanov homology is huge, but can be replaced by its deformation retract which is essentially smaller than the original one.