You can easily export your current project to MP3 via the "Export audio" option in the "File" menu of the program. One of the available output formats is MP3. It requires that the MP3 encoder was activated in the first place or that the program found an existing MP3 license it could use. If necessary, you can activate the MP3 encoder via the "Help" menu.
That said, exporting to MP3 doesn't have anything to do with burning to CD, though, unless you mean you want to compile MP3 files on your hard drive, which you could later burn onto a data CD. If you want to burn a regular audio CD that will play on most any CD player, just switch to the "Export" stage of the program and choose the "Audio CD" option.