If you are talking about audio optical out, then you need a DAC in order to connect the audio optical out from your computer to your receiver.
In fact, most receivers have optical in. You just need to plug the optical cable into that optical in.
If you receiver is of an older type that does have an optical in, then you need an external DAC (digital to analog converter).
Keep in mind the quality of the DAC greatly affects the quality of the analog signal generated
Most standalone DACs are quite pricey. Your best bet would be to spend about $200 on a cheap receiver that has an optical in.