When all of the egg (that covers the whole pan) is cooked, use your spatula to flip one half of it over the other half. Then let it cook just a bit more, so you're sure the inside is done.

Wish I could draw a picture--it would explain this much better.

Here, try this link. Maybe this will help clarify my explanation.
http://www.everydaycook.com/recipeb...fast/omelet.htm