You often have to change the output from your graphics processor to HDMI output, some will recognize it automatically but not all.
So plug the cable into your TV and Laptop, use the "Input" function on your TV to select HDMI if it doesn't auto recognize. Then you will have to go to the graphics properties in your laptop, how you do this depends on what graphics processor you are using, if its on an intel processor with built in graphics, for example, it will say something like "Intel hd graphics" when you right click on the "desktop" open this and there should be an option to set up multiple displays or similar. As I say it depends what graphics you are using, but play around with the options and you should find it.