Put in a DVD and start "Play".
Now, using the "menu" button on the TV remote, select the appropriate input source (eg AV1, AV2 etc).
You'll know when you've selected the correct input 'cos you'll see the DVD output on the screen.
Using a SCART cable if possible (instead of RCA/Component) is much easier as most TV's can switch to SCART input automatically when DVD player is switched on or when DVD starts to play.