How do I hook up my 55 inch led tv to a stereo for better sound

Connect tv audio out pin to stereo;s audio input pin

In many cases newer tv's do not have an audio out, some have a headphone jack on the side (Small usually blue)

Otherwise if you are wanting to get better sound from a DVD / Blueray / Satellite / Cable box, You can put the audio from these devices into your sound system, then plug your sound systems audio out into the tv.
The video out from your devices will need to connect directly into the tv.

If using HDMI or S-Video that carries both audio and video, slitter / separation boxes are available, but usually degrade sound and audio quality.

The above would look something like

Cable box audio out (red / white) to Stereo audio IN. >> Stereo Audio OUT to TV audio in.
Yellow (Video) Cable from cable box then goes directly to the TV Video IN. Just make sure the audio and video cables are going to the same section (Some tv's may have multiple audio / video in's