When adding citations to your document, you can use the default citation dialog box or the classic Add Citation dialog box.
Using the citation dialog box, select your item from the list. Before hitting enter, click on that item and another dialog box will appear. Here you can
Add more than one reference to the citation by continuing to type an author or title into the citation dialog choose another from the list. If you accidentally hit enter before doing this, double click on the citation in your document to select it and then choose Add/Edit Citation from the Zotero menu. The citation dialog box will reappear and you can make your changes.
To switch to the classic Add Citation dialog, check the option at the bottom of the Cite section in Zotero settings.
Now when you add a citation a window will open that mimics your Zotero library. Choose the item you want to cite, add a page number (or other unit), and any prefix or suffix you want to add. Use the Muliple Sources option to choose more than one citation. When adding notes and page numbers, be sure the correct citation is selected in the right pane.
Updating Citations
If you add a ciation to your paper and then realize something needs to be corrected, return to Zotero and make the change to the item in your library. Do not edit the citation in your document. Doing so will break the connection between the citation and its item in your library. After you make the change in your library, return to the document and click on Refresh in the Zotero menu.
Controlling the font style/size of citations
It is your word processing software, not Zotero, that controls the way your citations appear in your document. To modify the style in Word:
Go to Home > Styles > Options > Show all Styles
In alphabetical order, find Footnote. Footnote reference is the number style. Mouse over footnote text, click on the down arrow, choose Modify, and then change the formatting options. the default is to make the changes only to the current document.
There does not seem to be any way to automatically set a font format/size for footnotes in Google docs. You will need to select each one and change the formatting.
You can apply rich text formatting by manually adding the following HTML-like tags to fields in your Zotero library:
<i> and </i> for italics
<b>and </b> for bold
<sub>and </sub> for subscript
<sup>and </sup> for superscript
<span style="font-variant:small-caps;"> and </span> for smallcaps
<span class="nocase"> and </span> to suppress capitalization rules (e.g., for foreign phrases within English titles)
Zotero will automatically replace these tags with the specified formating when it outputs the citations/bibliography.
Some citation styles, such as the Chicago Manual of Style, convert titles to title case. However, title casing is specific to English. To prevent non-English titles from being title cased, specify the language of the corresponding item in your Zotero library using the “language” field.
Use two-letter language codes, e.g. “en” for english, “de” for German. see https://github.com/citation-style-language/locales/wiki for a list of locale codes).