In the theoretical part, I present basic concepts of Einstein's general theory of relativity; the mass, the priciple of equivalence, the gravitational field and space-time. I explain the motion of a body in space-time and the properties of Schwarzschild's geometry of space-time. I further describe classification, formation, structure and detection of black holes. I review didactic recommendations of some authors for introduction of Newton's and Einstein's models of gravitation, the weight, the principle of equivalence, weightlessness and the black hole. I focus on Einstein's theory of gravity and how to mimick it by using a flexible sheet. I also expose some deficiencies of such a model and misconceptions that can arise from it. In the empirical part, I review curriculum and textbooks for physics in elementary school. I prepare activities and simple experiments to introduce Einstein's theory of gravity, appropriate for elementary and high school. Using a gravity simulator composed of flexible sheet and balls I demonstrate effects of gravity and the concept of escape velocity, so that pupils can get a general idea of the black hole. I also use a map of the world in Mercator's projection and a globe to introduce straight and curved trajectories. Weightlessness is demonstrated by an experiment - I drop a bottle with a sponge and a kilogram weight.
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