There will come a time that you need to turn left but another car will approach from the front. You may not cross his path in a dangerouse manner that can cause an accident. The rule is you need to wait for all oncoming cars to first pass you before you can continue turning

Example of the left turning rule

The following intersection allows cars to turn left when the light indicating traffic light is green. If the light is green the traffic light for oncoming vehicles will be red. If the light is not green you must wait behind the line

traffic light red left turn Left turn

If for example there was no left traffic light at this intersection (Only normal traffic lights). Then you are allowed to drive forward slowly till halfway into the intersection and wait until all the cars have passed you. When its clear of traffic then you can turn left