The following methods of working with footnotes in Zotero can be used separately, or combined:
Inserting a footnote
To insert a footnote, place the cursor where you would like the citation to appear in the document. Choose Add/Edit Citation from the Zotero tab in Word. Find the item you want by typing the author's name in the red dialog box that comes up. When you press Enter, Zotero automatically inserts a footnote with the chosen item. You can also insert multiple items by writing them one after the other in the dialogue box.
Note that the above only works if you are using a footnote style. Select a footnote style in Document Preferences, e.g., Chicago Manual of Style 17th edition (full note). If it is not clear from the name of the style whether it is a footnote style, try to find the style at https://editor.citationstyles.org/ → Search by name > View style; the type of style is listed below Citation format.
Writing text in the footnote
To add text before the item cited in a footnote, use the Prefix field. Find this field by clicking on Add/Edit Citation and then clicking an item in the citation dialog box. Text intended to follow the item can be added in the Suffix field. In this way, all text in the footnote is written in the citation dialog box.
This method is best suited for short comments which do not contain much text beyond the cited items. The method allows Zotero to automatically transform the entire footnote into an in-text parenthesis if you choose to switch from a footnote style to a parenthetical style. There are, however, a couple of potential issues:
Inserting a footnote
First insert a footnote manually, using the function References > Insert footnote (or short command Ctrl + Alt + F). Then place the cursor in the footnote at the bottom of the page, click Add/Edit Citation, and insert the cited item as usual.
Writing text in the footnote
You can add text in the footnote by typing it in the document outside the grey field which contains the citation. Add a new item in the same footnote, separated from the first by text, by placing the cursor where you want the new item and clicking Add/Edit Citation.
This method is best suited to texts with longer footnotes that have more discussion. However, there are some disadvantages: