Summarize this article:

It's important to do this before you plug in any speakers or audio equipment. Look for at least one of the following on the back or side of the TV.   RCA - A red circular port and a white circular port. RCA is known as "analog" audio.  Optical - A square (sometimes hexagonal) port. Optical audio is known as "digital" audio.  Headphone - The standard 3.5 millimeter jack used for most headphones. You'll usually see an image of a pair of headphones above this port.  HDMI - Typically used for combined audio and video. Some stereo receivers connect via HDMI. Your individual speakers will almost always have RCA inputs, with the left speaker using a white input and the right speaker using a red input. If you're attaching a soundbar-type stereo system, your speaker set will likely have an optical input. You don't need to use an audio receiver with a soundbar. Unless you're using a soundbar or computer speakers with your TV, you need to use a stereo receiver (or amp) to connect to your TV. Your receiver will have at least one of the following inputs:  RCA Optical HDMI For example, if your receiver only has an optical input and your TV only has RCA outputs, you'll need an RCA to Optical adapter. This also applies for TVs that only have headphone outputs, as you can buy a headphone-to-RCA adapter. You can usually find RCA, optical, HDMI, and headphone cables and their accessories online, but most tech department stores carry them as well.

Summary:
Turn off and unplug your TV. Find your TV's audio output slots. Check your speakers' input type. Check your receiver's input type. Determine whether or not you need an adapter. Buy any cables that you don't have.