Mars has less gravity than Earth. Therefore if you were on Mars you'd weigh less because the force of gravity wouldn't be as strong as it is here on Earth. You would have the same amount of mass as you do on Earth. So, on Mars, your mass would be the same as it is here on Earth. But you'd weigh less because Mars has less gravity than Earth.
Gravity is an attractive force.
This doesn't mean it's pretty. The Earth's gravity naturally pulls us, and everything else, toward the center of the planet, which keeps us from drifting off into space. The Earth isn't the only thing that has gravity. In fact, every single object in the universe has gravity. The tables you're sitting at have gravity.