Now let's work on your MP3s. MP3 (.mp3) files need to be converted into wave (.wav) files before they can be burned to an Audio CD. Note that you can actually burn them to CD as data files, and fit many many more onto your CD, but you will only be able to play that CD in your computer or in a new-fangled CD player that most of us are not lucky enough to own yet. If you want a regular CD that will play in most stereo systems, you'll need to convert your MP3s.
There are two ways to put MP3s on your Burn List. The first is by choosing File->Open... in the Edit window of RipEditBurn Plus. Select the file type ".MP3" in the Open dialog box. Browse to the location of your chosen MP3 and click Open. RipEditBurn Plus will convert the MP3 to a wave file and open it in the Edit window. Do any editing you need to on this file (refer back to step 4 if you need to) and then save your final version in that folder on your desktop. Add this track to your Burn List by clicking the Burn tab with this file still open. Repeat this step until you've added all the MP3s you want to your Burn List.
The second method is to go directly to the Burn window and click Add Track. Select the MP3 and hit Open. The MP3 will be added to your Burn List and automatically converted during burning. Once again, though this method is faster and easier, remember that you won't be able to do any editing to tracks added this way.