When you download Zotero, you automatically also download a plug-in for Microsoft Word and for LibreOffice. The plugins allow you to "cite while you write": as you are writing your paper, you can create in-text citations by importing from your Zotero collections, and you can automatically generate a bibliography from these in-text citations. If you make edits to any Zotero entries, you can refresh Zotero in your Word document and your citations and bibliography will update and reflect any changes you made in your Zotero databases.
For more information on using the Word or Libre Office plug-ins, see the Zotero documentation.
If you begin a paper using the word processing plug-in and decide to abandon it, you can 'finalize' your document so that the in-text citations appear as they should, and then proceed to write the rest of the paper in the non-Zotero way. You'll have to create the rest of your in-text citations the old-fashioned way, and then generate your bibliography from Zotero itself, not automatically from your in-text citations. If you have all the citations you need for that bibliography in one collection, generating a bibliography will be easy.
Zotero can also be used to some extent with Google Docs.