Zotero offers word processing plugins for Word, OpenOffice (aka LibreOffice) and Google Docs. The plugin adds a Zotero toolbar to your word processor that allows you to add citations to your document while you write.
MS Word
LibreOffice
Google Docs
Change bibliographic styles in your document with the "Document Preferences" button.
This is also where you can add additional styles to your Zotero program. Click the Manage Styles link to go to the online Zotero style repository. Find the style you need and click on it to load it into Zotero.
To add a citation, put your cursor where you want it to go, and click the "Add/Edit Citation" button on the toolbar. In the red Quick Citation pop-up tool start typing the author name or title of the citation you want. Select the reference you want to cite and click the Enter key on your keyboard.
Or, you can use the 'Classic View' to see which collection you're choosing a reference from. Click the Z in the pop-up box to bring up your Zotero library.
After choosing your citations, your document will look like this.
At the end of your paper, click the "Add/Edit Bibliography" button and your bibliography will appear. Any new citations you add will be added to the bibliography automatically.
Multiple Citations
From the Quick Citation box, add multiple citations by entering them separately in the box.
In Classic View click Multiple Sources at the bottom of the pop-up box. Then send each source to the column on the right with the arrows.
Add page numbers
Put your cursor in the in-text citation, then click Add/Edit Citation in the document's command bar. The red Quick Citation box will pop up. Click the citation and it will show a box to enter the page number.
If you use the Classic View you can also add page numbers at the same time you select your citation.
To create a bibliography from your Zotero library select the references you want to include. Right-click the selected items and choose Create Bibliography.
Choose the bibliographic style you want, and select the output format.
Or you can do a Quick Copy and just drag and drop references from Zotero into your document. You can also select items and pres Ctrl+Shift+C to copy them to the clipboard.
Set your default style in Preferences | Export.
There are currently 2 annotated styles available from the Zotero Style Repository, Chicago and APA.
For the Chicago Annotated style, you put the annotation in the "EXTRA" field in the Zotero record (see screenshots below).
For the APA Annotated style, you put the annotation in the "ABSTRACT" field in the Zotero.
Chicago style
First, annotate the reference in Zotero.
Select the references you want for the bibliography
Export the bibliography from Zotero using the Chicago Annotated style.
Here is the bibliography with annotations.