When you listen to digital music, your software or hardware player usually shows information about the current song, which it gets from MP3 tags or Ogg Vorbis comments. Most ripping software supports acquiring this metadata from the CDDB or FreeDB services based on a CD's disc ID. But you can also can fill in and edit metadata with tools such as EasyTag and Picard.
EasyTag allows you to manipulate metadata in MP3, MP2, MP4/AAC, FLAC, Ogg Vorbis, MusePack, Monkey's Audio, and WavPack files. It has a GTK+ GUI and is available for GNU/Linux, Mac OS X, and Windows. And, as you might assume from its name, EasyTag is easy to use.