Adding/Assigning Tags

I'm following the directions to add/assign tags to documents, but they are not showing up in the tag category that I have assigned them on the left side of the screen.

What I'm doing is selecting the check mark box of the file I wish to tag. I then choose the tag that I wish to assign from the drop down menu. But when I click on that tag category on the left side of the screen, the document does not appear.

I would really appreciate help on this.

Thanks.