Once you've created a reference list (i.e., bibliography) the entries can be edited manually, but it's better practice to correct any mistakes within Zotero and select Refresh.  Another option is to select Add/Edit Bibliography which will now open in editor mode to make specific changes to your extant entries.
Of course, you first need to have references in Zotero before adding them to your document.  The following section will cover a few options for accomplishing that.

Adding References to Zotero

There are a variety of way to add items into Zotero.  I will cover three common ways here: manual entry, entry with identifier, and RIS import.
A word of caution is appropriate here before moving into the mechanics of this process.  Zotero, or any reference manager for that matter, is not a replacement for knowing the citation style and writing conventions of your field.  You will occasionally need to edit the references generated by Zotero, and will certainly need to know what information is required (and what can be omitted) when creating an entry in Zotero.  This requires that you understand how to reference common sources such as books, journal articles, conference proceedings, and websites.  It's easier to build a well-curated corpus of references from the beginning than it is to correct previous mistakes.
1. Manual Entry.  Manual entry is the most cumbersome way of creating a reference, but sometimes other options are not available.  Simply select the green + icon and choose the appropriate reference type from the drop down as show in Fig. 9.  Most common reference types are listed here; and Zotero will provide your most frequently used types at the top of this list.