With Zotero for Firefox, you can create an item from the current website by either clicking the Create New Item from Current Page button above the middle column of the Zotero library middle column, or by right-clicking the website page selecting Create New Item from Current Page from the Zotero menu.
With Zotero Standalone, you can create an item with snapshot from the current website by right-clicking the page background and selecting Save Zotero Snapshot from Current Page.