The Ant wanders around on a "inifinite" square grid. Everytime it comes to a square, the square changes colour from black to white or from white to black, and if it lands on a white square it turns right, but if it lands on a white square it turns left.
This is the Ants universe.

During the first two or three hundred moves ff the Ant, starting on a completly white grid, it creates tiny little patterns which are very simple and often very symetric. And you sit there thinking 'Of course, we've got a simple rule, so that will give simple patterns, and we ought to be abel to describe everything that happends in a simple way.

Then suddenly, you notice it's not like that any more. You've got a big irregular patch of black and white squares, and the Ant is wandering around in some sort of random walk, and you can't understand the structure at all. For langtons Ant this kind of pseudorandom motion happens for about the next 10.000 steps. So if your computer is not very fast you can sit there for a long time saying 'Nothing intresting is going to happend, it's going to go on like this forever, it's just random'. No, it's obeying the same rule as before.
It's just that to us it looks random.

Finaly the Ant locks into a perticular kind of repetitive behaviour, and it builds a 'highway'. It goes through a cycle of 104 steps, after wich it has moved two squares diagonally and the shape and the colours along the edge are the same as they were at the beginning of that cycle. So that cycle repeats forever, and the Ant just builds a diagonal highway - for ever.