In iTunes goto edit->preferences and click the advanced tab, following by the burning sub-tab. Make sure it's set to audioCD if you want to create a regular audioCD.
then create a new playlist by clicking the bottom-left plus button, and drag the music you want from your library into that playlist. you'll get about 80minutes of songs onto the CD since it's an audioCD, but when in the playlist iTunes will tell you how much you've got anyway. Once you're ready put in a blank CDR disc into your burner and click the top-left burn button.