Plugging in the power to the card and turning on the computer won't damage anything. You are going to have to change the format of your video output. You should plug a monitor, if you have one, into one output on the card and plug your TV into the other. More than likely your monitor will be able to handle the format so you can see when you change the format on the TV. To change the format on the tv you would have to go into the Catalyst control center. On the left pane you will see digital flat panel. Choose the format that your TV says it can handle with HDMI.
Hopefully this helps