Click on in the tag editor to open this window.

There are several sites where album information and / or album art can be downloaded from. MP3 Diags can currently talk to MusicBrainz. It used to be able to talk to Discogs as well, but that currently no longer works and the corresponding button has been disabled. The screenshot above is for Discogs, but MusicBrainz is quite similar. Going to MusicBrainz is the preferred method for getting album info. If you don't find what you are looking for, adjusting the query manually may give you better results. If you can't find your album, you may want to search the internet for the track list; if you find it, chances are you can import your data by simply pasting the text from the clipboard in the main Tag Editor window (that is, provided that you defined appropriate patterns.)