The Compressor dropdown contains a list of available compression formats to compact the data in your audio and reduce your filesize.
The Rate is measured in kiloHertz, and basically determines the audio quality. Increasing or reducing this number will increase or reduce your audio quality, and also your file size.
The Size differentiates between 8-bit and 16-bit streaming audio. Obviously 16-bit is larger than 8-bit, but also has better sound quality.
Use is split between Mono and Stereo; mono audio treats all sound as a single track, and will play the same sounds from all speakers attached to your computer regardless of how many there are. Stereo, however, can split the tracks so that some sounds play from the left speaker, some from the right, and enables effects like a side-to-side audio fade.
Your Options button will remain greyed out unless you select a compressor. There are too many compressors to go over in detail in this lesson, but their options are fairly similar to those offered under the basic Sound Settings. Try experimenting with them to see what results you get.
Once all of these options are set, you can click Ok to exit the Sound Settings, then Ok again to exit and save your Publish settings.