Audacity will have already pre-scanned your file and Amplify will default to whatever gain is needed to maximize/normalize your file, so just accept the default and click OK.
Note that it will use the “loudest” peak in the file, so the overall volume may not be enough. If it’s not loud enough, you can run Amplify again, but this time set it to allow clipping (distortion) and adjust the gain as desired. If that doesn’t work, or the distortion is not acceptable, let us know and we can give you some more “tricks”.
Also of course, when you boost the volume you also boost the background noise.
Ripping the data from a CD produces much better quality than recording from a loudspeaker.
That’s only if you have a regular audio CD. If you have a WAV file on the CD you can simply open it in Audacity or copy it to your hard drive.