This is easier to explain with math, than with a demonstration. Space never ends in the same way the surface of the earth never ends. It's not that the surface of the earth is infinite, but if you keep going far enough you end up in the same place. The visible universe is huge, though, and the whole universe is even bigger. So much so that we will never reach the "edge" where you end up where you started. If you could walk through space in a perfectly straight line, in many billions of years you would end up back at Earth. So space "never ends," but it is finite, like the surface of the earth.