The display of the Zotero extension has three columns: the first is the Library view, the second shows each item within the collection, and the third shows the metadata for the item that is highlighted.
In the 'My Library' view, you can organize your citations into collections and subcollections (think of itunes playlists..this is similar). Once you've created collection(s), drag and drop items into each collection. The items will always be in your 'My Library' collection, even if you delete them from a collection, or if you delete the collection entirely.
You have the option of adding two types of notes:
To add a note, click this button (found in the toolbar) and select which type of note you'd like to add:
You can also add child notes by click on the 'Notes' tab in the right-hand column. Click the 'Add' button and begin typing your note.
Tags can be attached to items in two ways. First, tags may automatically be attached when you add an item into your library (i.e. when adding an item from the library catalog, the subject headings for the item will appear as tags in Zotero).
Or, you can manually add your own tags to items by selecting the 'Tag' tab in the right hand column (next to Notes). Click 'Add' and enter any, and as many, tags as you'd like.
Tags are searchable and can be a useful way of grouping items together.