If your Macintosh has a CD burner that works with iTunes, you can create your own audio CDs containing the songs in a playlist. iTunes converts the songs to standard audio files before writing them to the CD. You can fit about 74 minutes (about 20 songs) of music on an audio CD (depending on the settings you chose when you imported the song into iTunes).

Choose Preferences from the iTunes menu. Make sure Audio CD is selected in the CD Burning tab, then click OK.
Select the playlist you want to burn to the CD, then click the Burn CD button. Then insert a blank CD-R disc in your Mac and click Burn CD again.
It takes several minutes to write an audio CD. You can cancel the burn by clicking the X next to the progress bar, but since you can only use CD-R discs once, you might not be able to use the CD after canceling.
The songs sound as good as they do in iTunes. Songs you download from the Internet may be encoded differently, so their quality may be different.