Final answer:
To make a left turn, extend your left arm horizontally out of the window, which clearly signals your intention to turn left.
Step-by-step explanation:
If you are trying to make a left turn, the correct hand signal to use is to extend your left arm horizontally out of the window. This means your entire left arm should be straight and level with your shoulder, pointing to the left side of your vehicle. This action clearly indicates to other drivers and pedestrians that you intend to move left or turn left.