Finding Items with Tags
Tags, or identifiers, can be added by hand or automatically imported when you import citations.
All tags currently in your library are listed on the bottom left of your desktop Zotero.
To see tags affiliated with a particular item, click on its name and select "Tags" from the choices on the right (desktop version), or from the "Tags" tab at the top of the screen (web version)

To see articles affiliated with a particular tag, click on the tag and Zotero will show you the articles in your Library that include that tag.