When you are ready to add your bibliography / reference list, simply click the Add/Edit Bibliography button from the Zotero menu. This will create a bibliography using all of the citations from your paper in the format that you specified earlier.
This pulls in only the citations that you used cited in your paper, but if you would like to add or remove citations from your bibliography, click on the Add/Edit Bibliography button again to bring up the Edit Bibliography menu. This will allow you to manually add or remove citations from your bibliography.
You can also generate a bibliography from within the Zotero app. This is helpful if you need to copy / paste citations, such as enter citations into a Canvas discussion board. You can either highlight all the items you would like to cite, then right-click and select Create Bibliography from Items. If you want to cite everything from a collection, you can simply right-click on the Collection folder to Create Bibliography from Collection. From there, you can choose to download your citations to RTF format, or copy them to your clipboard (for pasting into another program).