Looking for a good ID3 tag editor for Windows? Check out AudioShell. (If you aren’t familiar with ID3 tags, they include metadata that tells your media player things like the track name, the artist, and the genre. That’s how your MP3 player can know how to play all your jazz tracks.)
This software is free and includes the ability to add cover art to your file. You can edit single files or groups of files with this tool. Once it’s installed, you edit the tags by right-clicking the file and selecting Properties. There you’ll see an AudioShell Tag Editor tab where you can edit your tags.