These belts are formed by trapped charged particles. The magnetic field traps these particles from the Sun. They then spiral around the lines of the Earth's magnetic field, going back and forth between magnetic poles. These radiation belts are dangerous to astronauts. Shuttle missions are planned to stay away from the harmful particles as much as possible.
Gravity is the pull that one object exerts on another.
The more mass the object has, the more pull it exerts. The Sun is so big, it pulls all the planets into orbit around itself. The Earth is so big, it pulls you down so you don't float away. That's gravity . Everything clouds are made of falls to Earth.