Logically for three lanes leading to two lanes after the round about these are to be followed

In LEFT lane you turn left or go straight to left lane of the two lane road
In MIDDLE lane you go straight to the right lane of the two lane road
In RIGHT lane you turn right or go straight to right lane of the two lane road.

Here however there can be exceptions to the rules depending on how the traffic is and your driving skills. You may turn to take the left from the middle lane provided there's no on coming traffic from your left side wanting to go straight and you must give Left indicator BEFORE you enter the round about.

You may also get into the left lane of the two lane road from the middle lane again depending if there is no car to your left.

You will be then wondering what do the cars on the RIGHT do if there is a car in the middle lane wanting to get into the right lane of the two lane road. Qatar rules simply says ALWAYS GIVE WAY TO THE TRAFFIC ON YOUR LEFT.