What is the difference between CD-r and CD plus r discs?

There are two competing formats for DVD's + and - format. Your question doesn't mention the + so they are the same format - or the lack of + means -. DVD + is technically a newer format but that doesn't make it any better than the -. You need to determine what your computer's drive burns and also what your DVD player plays. Some computer drives burn both formats. The R stands for Writeable meaning you can burn information or a movie only once. Most newer DVD players can play any format but some cannot. Check the manual or just use trial and error. As a Word of advice don't buy a 100 pack of DVD's without first testing your system to make sure they are compatible. Buy a single CD or a smaller pack until you have verified all is well with your system.