Newtonian theory, which held sway prior to the 20th century, described gravity as a force. In other words two massive bodies like the Earth and an apple were understood to exert a pull on each other as a result of the law of gravity. If an apple started out at rest, say just as it broke off from a tree, then gravity would cause it to move towards the Earth until it collided with it. Newton's law of gravity was able to explain in detail not only the fall of apples, but also the orbit of the moon about the Earth, the motions of the planets about the sun, and much more. GR can also explain all of those things, but in a very different way. In GR, a massive body like the sun causes the spacetime around it to curve, and this curvature in turn affects the motion of the planets, causing them to orbit around the sun.

http://www4.ncsu.edu/unity/lockers/users/f/felder/public/kenny/papers/gr1.html