If your computer has a HDMI port, you will need to get a HDMI cable and connect it from your TV to your computer.
If you have a Mac, you will need a HDMI adapter that plugs into the thunderbolt port since most macs don't have a HDMI port (the new macbook pro with retina does, as well as the mac mini I believe). Monoprice.com sells their own brand cheap but I believe you can also buy them from Apple. I have the monoprice adapter and it works well.
If your computer doesn't have a HDMI port you may be out of luck for now unless your TV has a VGA input for PCs. Many TVs do. Or if your computer has a DVI port you can get an adapter to connect to HDMI. Audio may/may not work. It really depends on the computer.