Items placed into your Zotero library can be organized into collections and sub-collections. This function allows you to organize your research in meaningful ways. Click on the pale folder icon to add a new collection. To create subcollections right click on the title of a collection and select "New Subcollection".

The Zotero browser plugin allows you to choose which collection to save items into. A reference can be in more than one collection at a time.
Zotero has a built in PDF reader where you can read and annotate your sources. In PDF reader you can highlight, add comments and create notes from your annotations.

To turn your annotation into a note, select the notebook icon in the upper right-hand corner of the reader. This will open a panel where you can create the note. On this panel click one of the “+” buttons and select Add Item Note or Add Item Note from Annotations.

Tags help make your library searchable, allowing you to pull up all items related to a topic. Sometimes tags will be automatically generated from subject headings and keywords used by a database or website.

You can create your own keywords using the browser plugin or in the Zotero app. Remember to be consistent when creating tags to make full use of this feature.