What does gravity do in space?

Gravitational pull decreases with the square of the distance to the planet's center, not with height above the ground. Since Earth's average radius is about 6,371 km, climbing 400 km moves you only about 6% farther from that center — which is why acceleration there is still around 90% of the 9.8 m/s² measured at sea level. Someone weighing 80 kg would read about 72 kg on a scale fixed at that altitude. To truly leave Earth's gravity behind you would need to travel much, much farther, and even then the Sun, the Moon and the rest of the galaxy would keep pulling.

What we call weightlessness is continuous free fall. The International Space Station travels at about 28,000 km/h and circles the planet every 90 minutes: its path curves at exactly the rate the Earth's surface falls away beneath it, so it never catches up. The station and its crew fall together with identical acceleration, so no one pushes against the floor and the floor pushes back on no one. The same sensation is reproduced for a few seconds in aircraft flying parabolic arcs, without ever leaving the atmosphere.

Gravity keeps the Moon in orbit, bends the path of probes flying past a planet to gain speed without burning propellant, and defines the Lagrange points where space telescopes are parked. Aboard the station only a tiny residual acceleration remains — vibrations, drag from the thin residual atmosphere, reboost maneuvers — hence the term microgravity. That environment is precisely its scientific value: without convection or sedimentation, flames, fluids and crystals behave in ways impossible to reproduce on the ground.