At one time, burning a CD or DVD was great for backing up stuff, transferring stuff to another computer (even a Windows PC), mailing to somebody, or offloading (archiving) older files to free up hard drive space.
These days, those discs are too small to use for backups or archives, too slow to burn for transferring files, and ridiculous to send by mail. WiFi and Internet services have deprived CDs and DVDs almost completely of their few reasons for being.
But OS X Yosemite can still burn those discs, if you buy an external disc drive. In that case, the free downloadable appendix to this chapter, “Burning CDs and DVDs.pdf,” offers step-by-step instructions. You can find it on this book’s “Missing CD” at www.missingmanuals.com.