When you find a source you would like to save the citation for, click on the connector button. In the lower right corner you will see a pop-up indicating that Zotero is saving your citation.
If you want to save the citation for a hard copy item, look up the item in the catalog or database first. If the item exists in the database/catalog/online you can grab the citation using the Connector.
If you can't find the item online, you can create a new citation manually. First, click on the green plus sign icon and choose the type of source you want to create a citation for from the drop-down menu.
Next, fill in the fields in the new citation you have just created.
To edit existing citations, just highlight the individual reference you wish to edit, select the field wish to add to edit, and type in your changes.
When you install Zotero, it automatically includes only a few of the most commonly used styles out of thousands of formatting styles. If Zotero does not have the formatting style you need, just visit Zotero's Style Repository, on your desired style, and save it to your Zotero style library.
The style will be uploaded to Zotero and available for you to use.