It's not hard to use, but it can be a little chaotic in the beginning if you have lots of audio files. Once you tag the first one, though, it becomes a piece of cake.
MusicBrainz Picard lets you manually change your files' ID3 tags. If you think that might be too much work, you can access MusicBrainz's huge database on the Internet, which will automatically search the names of the audio files to get the information you need. From there, MusicBrainz Picard uses that data to automatically tag all your files and save them with their original names.
If you think tagging your entire music library is a complicated and difficult task, MusicBrainz Picard can be a huge help. With it, you can name and organize your entire music collection without too much hassle.