How astronauts move about in space

As you know, unlike Earth, the space has no gravity. Then how do astronauts move about in space? And why? Astronauts may have to repair or fix satellites or space stations. So, they have to be out of their space shuttle. They need to move. As there is no gravity in space, there is danger of astronauts flying off into space.  So, they use handles and special footholds (into which feet can be locked) to move in space safely. But sometimes, they may have to fly further away from their shuttles. For this reason, astronauts use special backpacks which have rockets built into them. These backpacks are like floating armchairs which are controlled by a hand-held device like a joystick. These backpacks are powered by nitrogen gas thrusters.