The Zotero Interface
Zotero's interface is composed of three columns moving left to right from general to specific:

(Note: This image is of Zotero after citations have been added. When you first install Zotero your library will be empty.)
The center column displays the list of your citations. You can limit/sort the items that show up here by selecting a collection on the left or by searching for keywords or tags.
The icons at the top allow you to manage items, notes, and attachments in your library:
New Item
Create New Item From Current Page
Add Item by Indentifier
Add new citations.
New Note
Add notes to your library. Notes can be either Standalone or Child Notes (attached to a specific citation).Hint! You can select text in your browser and drag it into the note's text box when composing a note.
New Child Attachment
Attach a file to a citation in your library.
Once you add notes and attachments they will display nested under the citation: