Find and mark a point on Earth that's the same distance from the north and south poles. Then find and mark another one. And another one. And another and another and another one. Then find 10,000 more points like that. Then find and mark a million more points like that. When you've marked enough of those points that are the same distance from the North and South Poles, they'll begin to blend together and look like a line around the whole earth. That line is the equator.
