With the general theory of relativity, in which Einstein managed to reconcile relativity and gravitation, he had to discard the traditional physics worldview, which saw space as merely a stage on which the events of the world unfold. Instead, space-time is a dynamic entity, which is distorted by any matter that is contained in it, and which in turn tells that matter how to move and evolve. This interaction between spacetime and matter is described by Einstein's geometric, relativistic theory of gravity.
The consequences of that theory are spectacular. For instance, general relativity predicts that even light is deflected by gravity - a prediction that has been confirmed by numerous astronomical observations. In addition, it predicts exotic phenomena like gravitational waves and black holes, which are described in later sections of Einstein Online.