what do i use this for?

It's basically a sorting tool.  You can tag a book with  paranormal fiction.  If you would click on a tag, it will bring up all the books that are identified as such.

The tag button on books? Those are to make notes about the book that everyone can see (unless they have tags turned off).  Some people use it for personal tags. I have some tags for me so I know what books I have on ebook-I use my dogs name-ebook.  So no one thinks someone is trying to list ebooks here. I also have a tagged list of some of my unpostables for the Damageed books box.  Again I use my dogs name-unpostable.  You cannot just tag a book unpostable because then it sounds like it applies to all the books. Some members have tried to tag books like "water damaged" or "smoking home" thinking they're informing the person who orders the book but it doesn't work that.

Then you can tag books with useful public tags. Like Highland Romance or Nevada ( for books that take place in Nevada) stuff like that.

It will only bring up books that someone has tagged with that tag.  Not necessarily everybook that fits that category.

There is also the note button.  Which makes a yellow square over the book cover.  This is to make a note that only you can see.  I use those to describe where the book is.  The library, the bookshelf, the box under the bed, the back room.

I love the note button. So handy. I use the notes to remind myself of things about that book. That way my personal notes about a book, won't show up on that title for everyone to see, like a tag would.  I like Club Useful tags.

I use the notes a lot too. THe only problem with notes is that you can't bring up a list.  But it's great for things you don't need to see in a list form. I do the Damaged Books VB and tag some of my unpostables for that. Then the other players can see what I have. I use the note feature to mark the ones that I'm not ready to add to the public list.

I also use the note feature to mark how many copies of a book are posted and track WL movement on my TBR books.  I wish people would use the notes instead of tagging their position in line for WL books.