The image to the right is a good one for showing how the road markings on spiral roundabouts are supposed to work.
Now imagine you are driving onto the roundabout. Look at the lines that are formed by little white dots. These are temporary lane markings which help you to find the lane on the roundabout that corresponds to the lane you approached in. Anyone that's approaching in the left lane is guided around to the left. Anyone approaching in the middle lane is guided to the middle. Anyone in the right lane is guided to the right lane of the roundabout.
This roundabout has dotted lines at every point of entry. The dots are only for people joining the roundabout. Once you've joined, you can safely ignore the dots.
Staying in lane
Now that you are on the roundabout and in the correct lane (the one that corresponds to your approach lane), all you need to do is continue following the lane you are in. This is just like lane discipline in normal driving: don't cross the white lines either side of you unless you have a good reason. You will not normally need to change lanes on a spiral roundabout. If you do need to change lanes, make sure you check it is safe before you do so. Signal if necessary.
Once you are following your lane, it should guide you off the roundabout and into the exit you were looking for. As you follow the lane, keep an eye on the road markings to confirm you are still on course for your destination.
