Once Zotero is installed, you'll see an icon in the top right corner of your browser window (Firefox) or your address bar (Chrome) whenever you're on a page with source that can be added to Zotero. Find one of each of the following items and add it to Zotero:
You can also add items to Zotero manually via the New Item menu.
To add a file to an existing Zotero item, drag and drop from your computer to the Zotero item.
Select the New Collection menu to create a collection. Drag and drop items from your library into the collection.
Right click on any item in your library to add a note. Zotero will store your note as an attachment to that item.