Decide what information you will use to identify each CD. For example, you may use file fields alphabetically by artist or composer name, and assign the same field in the same place on each card. Alternatively, you may number your index cards, and have a list or second set of cards by number cross-referenced alphabetically to your numbered cards. The numbering method has the advantage that you will not have to change the cards around when a section gets full, making the cards unable to fit in your box.
Choose a music library program for your computer that will contain your uploaded or downloaded CDs. One common program is iTunes, which will organize and catalog your CDs for you. In iTunes, choose "Preferences/General" and check the box so that the program will retrieve track information for your CD. Then choose "File/ New Playlist/" and choose a title for a folder containing music by artist, CD title, etc., on the left side of the screen. You may also choose "File/Add to Library/" to add all of your music to the main library automatically. Or, choose "File/Organize Library" to set options for subfolders.
Choose "File/Smart Playlist/" and pick an identifier field, like "Title," so the program will automatically put CDs with the same identifier in that "Smart Playlist." If you need to know more about the CD, choose "File/Get Info" for the CD you selected and you may obtain further information like the number of tracks, and label. If you are making a "Smart Playlist" from different CDs having several tracks, make sure you check off whether each CD is a compilation, and choose an identifier that is not dependent on the CD as a whole. For example, if you have CDs with a variety of opera arias and artists, you may choose to organize them by artist, title of aria or composer. If you are not clear about which music is on which track, choose "Advanced/Get Track Names."
Check which digital music library program is best for your computer, operating system, and compatibility with other music players you have, like mobile phones, digital music players, and tablets. Windows Media Player works in the same way as iTunes to organize CDs, although these programs are not identical. If you use another online music service it may provide its own music library system.