Why do planets orbit the way they do?

Tonight my five year old son asked me if the earth could fly into the sun and if not why? He said if there’s “no gravity in outer space and space men can fly around how come the earth doesn’t just move around in space.” And my answer was I’m not sure let me find out. So why does the earth hold it’s position in orbit with the sun and planets? Yes I took physics in college and no I don’t remember much.