Where can I find documentation on using TAGGER?
Not exactly sure what you are asking for, but we have documentation for Picard at http://picard.musicbrainz.org/docs/guide/ and related pages.
And I have written specifically about using the tagger icon on MB.org:
Are you familiar with the image above?
Are you familiar with the icon below?
He is, and he already answered regarding that:
I will look again and ask any follow-up questions I may have or simply say I am sorry and thank you.