In some cake and dessert recipes you have to seperate the yolks and egg whites from each other. The whites are usually beaten stiff and added at the end to lighten your batter (see tips in http://redcuisine.blogspot.com/2010/09/egg-white-disaster.html). For fresh handmade custards and custard-type desserts such as Crème Brûlée, you only use the yolks. Here is a very nice, easy recipe: http://www.cremebrulee.com/creme.htm
In Mastering the Art of French Cooking and in Julia Child's cooking show (available on DVD on Kalahari.net / Amazon.com / etc) she shows how yolks and sugar are beaten to form "a ribbon". This takes a little time and you know you're getting to the end when the yolks and sugar are beaten to a pale yellow colour. And when you lift the beater you'll see the mixture make a beautiful ribbon that falls gentle into the rest of it. Magnifique.