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.
Just asking, why are you trying to hook the laptop up to the TV using HDMI? You may want to just use Chrome Cast which will allow you to stream anything in your Chrome browser/laptop to your TV, without any wires...
I agree with RandomAdam. And if you find a switch that says something liike "mirror" display, check it. I got next to nothing from my HDMI connection until I did that. The switch was part of my video card software.