Your weigh is caused by the force of gravity. Gravity exists between objects that have mass. Because of the Earth and your mass, gravity exists between you and the Earth. It acts towards the center of the Earth pulling you down. Therefore, you feel your weight acting downwards. Astronauts feel weightless when the are in space because they are away from the gravity of the Earth. If they were to travel to another planet they would feel weight again. However, that weight would be different from their weight on Earth because the gravity of the planet would be different.