You have the display set in Extended Desktop mode. In System Preferences>Display on the MacBook screen there should be an Arrangement tab when you have the MacBook hooked up to the TV and both screens working. When you click the Arrangement tab do you see two monitors side by side? One of them will have a Menu Bar at the top. Just click on the Menu Bar and drag it to the second monitor. That will make the second monitor your main screen. You can now use your MacBook in Clamshell Mode with a wired or Bluetooth keyboard and mouse. http://support.apple.com/kb/HT3131 When you disconnect from the TV your Menu Bar will automatically change back to the MacBook.
Or if you want to work on the MacBook screen while showing it on a TV you can check the Mirror Display box on the lower left hand side of the Arrangement tab under the two monitors box.