Using graphene on hexagonal boron nitride (hBN) as an example, we introduce the concept of van der Waals heterostructures. First, we explain extraordinary high quality of graphene on hBN. Then we discuss the physics of formation of moiré patterns and a general problem of commensurability and incommensurability. We also discuss the basic consequences for electronic structure and electron transport properties, including a conductivity along zero-mass lines, formation of additional Dirac points and recently experimentally discovered new types of magneto-oscillation effects in graphene superlattuces.