There are a few different ways that you can get sound from your Nintendo Switch to your TV. The most common way is to simply use the HDMI cable that came with your Switch. If you plug this into the HDMI port on your TV, you should be able to hear the sound from your Switch just fine.
Another way to get sound from your Switch to your TV is to use a wireless adapter. There are a few different adapters that you can buy that will allow you to connect your Switch to your TV wirelessly. This is a great option if you don't want to have to worry about running a long HDMI cable across your room.