The DVD player has specific audio and video outputs that connect it to the HDTV. Your HDTV has various inputs (you don't use channels anymore unless it's REALLY old). Typical DVD Player outputs are:
S-Video - Single 7-pin (?) cable that carries both audio and video
Composite - Three RCA cables. Yellow for video, Red/White for audio.
Component - Five RCA cables. Red, Blue, and Green for video, Red/White for audio.
HDMI - Single cable with a D shaped connector.
Your HDTV should have each of these inputs. Figure out which DVD output you used and which HDTV input you used and then change the input source on your HDTV to that input. You should have picture and sound.
If you're still not sure, please provide us with the model numbers of...