It is ready to receive a HD signal.
Get a HD cable box, or Blu-ray player and connect it to the projector by either component video cables (red/green/blue) or by HDMI.
That'll get your HD video to your HD projector.
For audio, you will need speakers. Typically audio is handled by a A/V receiver and many speakers and you feed digital audio through HDMI or optical/coaxial digital audio to the receiver. Audio is a different subject you can ask about if you want/need to.
But, for video, just run video to the projector using a HD capable connection (component/HDMI) and use a HD source (HD Cable (or satellite) or Blu-ray Disc).
