A:Answer Let me start by assuming you have a DVD (portable or fixed) attached to your TV, and now you want the TV audio Transmitted to your Bluetooth headphones. If so, the instructions are included with the Transmitter. If the TV has 1/8" audio output, try that since it will probably mute the TV-speakers giving you the freedom to adjust the Volume with the TV remote. Pretty simple. If you have to use the Red/White RCA audio output then you may have sound coming from the TV and the BT headphones, but with the headphones on it may be ok for you...
If you are trying to catch the audio Directly-from the DVD player (to reduce audio latency?) then you are going to have to experiment a bit. Today's DVD players send the audio over with the video on HDMI, so the TV is responsible to sync them up; hence, audio from the TV will usually be easiest.
Btw, Some have suggested getting BT Headphones that have a "volume" adjustment built in. I use "'s because the adjustment may be limited to Attenuating (quieting) the volume only; powered amplifier in the headphone would be ideal but I haven't looked around to see if they exist yet.