Mass is the amount of matter that you are made of. Since you are made of the same amount of matter no matter where you are, your mass will stay the same if you go into space or even to other planets.
Weight is a bit different.
Your weight is the combined effects of your mass and the force of gravity. All things that have mass produce a gravitational force. The neat thing about gravity is that it becomes weaker if you move far away from the source. So if you were in outer space, there is less gravity, so you would weigh almost nothing. Another neat thing about gravity is that it is stronger if the source is more massive.