It will depend on your home theater system and TV. If your system accepts HDMI in from other devices and HDMI out to the TV, connect an HDMI cable from the blue-ray player to an HDMI input on home theater system. Then connect another HDMI cable between the home theater system and the TV. This will provide the best video and audio experience.
Another option is connect the HDMI cable from the Blue-ray player to the TV. Connect the audio output of the TV to the home theater system. (This will depend on the TV as well as the home theater system. Some TVs have digital audio outputs; others have analog outputs. If your home theater system doesn't have the same input as the TV's output, you would need a converter as well as the digital and analog audio cables. This is an example of one for digital to analog: http://www.gefen.com/kvm/dproduct.jsp?prod_id=4907
If you do not want to get the best picture from the Blue-ray player and your home theater system has analog audio inputs, you can connect the composite video out to the TV. Then connect the audio outputs from the player to your home theater system. (This means only an SD picture will be provided to your TV.)
Panasonic has the manual for the DMP-BD871 here: service.us.panasonic.com/OPERMANPDF/DMPBD871-MUL.PDF
I hope this helps. Please add a comment with the other devices in your entertainment system or their inputs/outputs. Then I can add specific information for your system and any tips for setting up the system.