Is it possible to automatically tag files?

I just downloaded MP3Tag to edit metadata to some of my music files. However, I don't seem to understand how it works.

Can it automatically update the metadata? Or must I select a service (Amazon, MusicBrainz etc) and then manually input album info to get the metadata?

What do you understand by automatically and by manually?
If you have tag-infos for artist/album you can mark your tracks for 1 album and call a webservice to fill in further tag-informations. I call this automatically because I don't have to write these informations myself to the tags.
If you do not have any tag-informations (artist/album) you have to mark your album-tags and fill in the search-field yourself in the process of calling a webservice.