"The Hitchhiker's Guide to the Galaxy states: "There is an art to flying, or rather a knack. Its knack lies in learning to throw yourself at the ground and miss." Both the ISS and its occupants are falling due to the Earth's gravitational field, but their tangential momentum means that they keep missing and so orbit the Earth. Since they are falling at the same rate, the occupants appear to float inside."

Wee hehe