I have an LG HDTV, directv, blu-ray player, and a PS4 with an ONKYO 305 RECEIVER. I have an optical input on my tv but cant us

Since that is a stereo receiver it can't process DD or DTS which are surround sound codecs. You can only reproduce 2 channels so if you are getting stereo then all is correct. If you can't get any sound then change the audio output type in the TV audio menu.