How do you make a left turn in a roundabout or traffic circle?

If you're in a country which drives on the right (e.g., United States, Canada, Mexico, any country in mainland Europe, etc.), you come to the roundabout and yield to traffic already in the roundabout before entering. You'll turn right into the roundabout once you're assured that there is no oncoming traffic, proceed 3/4 of the way around the roundabout, and execute a right turn onto the street you intend to go onto (as you'll be facing the opposite direction as you were when you originally came into the roundabout).

If you're in a county which drives on the left (e.g., United Kingdom, Ireland, Barbados, Jamaica, South Africa and most of southern Africa, Australia, Japan, etc.), you will still come to the roundabout, and yield to any traffic which is already in the roundabout. Once it is clear, you'll execute a left turn into the roundabout, proceed 1/4 of the way through the roundabout, and turn left onto the street you intend to turn onto.

Added: (in the US) To further complicate the entire matter - SOME states require the entering traffic to yield to the traffic already IN the circle, while others require the traffic already in the circle to yield to entering traffic. (!!!) Be sure you iknow the traffic regulations of your particular state.