It's a common misconception that there's no gravity in orbit — at the ISS's altitude, Earth's gravity is still about 90% as strong as on the surface. Astronauts float because the station (and everything in it) is in continuous free fall around the Earth, just like the satellite example above: they're falling at exactly the same rate as the station around them, so relative to their surroundings there's no sensation of being pulled in any direction — true weightlessness, not an absence of gravity.