Authors Unite is NOT a soccer team made up of writers (although that's not a bad idea). It is, instead, an index of Author Pages on Facebook, the brainchild of T.J. Forrester, author of Miracles, Inc.
More and more authors are creating "Author Pages" (what used to be called Fan Pages) on Facebook--a place to attract readers and to share news about books and other publications. It's one more thing we do to get the word out about our work and promote the sales of our books. (Mine is here: Clifford Garstang -- Author.)
If you are a writer with an Author Page, go to Authors Unite and add your page to the index. If you "Like" the page and begin to "Like" the pages of others in the index, gradually the number of "Likes" on your page will increase. (Most likely. Heh.)
And, if you are a reader, check out Authors Unite -- you may find information about some writers you weren't aware of before!