How do I extend my screen (instead of duplicating) when I connect macbook pro to my TV via HDMI?

When I connect my Macbook Pro laptop to my LG TV through HDMI, it only duplicates the screen which I also see through my macbook Pro. So essentially, I have two SAME screens on my both Macbook Pro and TV. I want to EXTEND the screens instead of duplicating the screen. Anyone know how to do this at all??? Is this just impossible?

Thanks for your answers!!!