When looking at an article you want to save to Zotero, click on the Zotero icon in your browser. This will prompt you to log in if you haven't already. Once logged in, you'll see a lightbox in the lower right corner of your page that confirms the article has been saved.

Go to Zotero to modify information about the item.

Once you're viewing your item, use the Zotero Connector icon in your browser to capture the document. Again, the lightbox will appear and confirm that the item has been saved to your collection.