Zotero's word processor plugins integrate Zotero into Microsoft Word and OpenOffice/LibreOffice/NeoOffice.
Different versions of Zotero require different plugin versions. Check your Zotero version if you're not sure which plugin to install.
Zotero Standalone: Word processor plugins are bundled with Zotero Standalone. More information is available in the Cite pane of the Zotero preferences.
If you experience problems with the word processor plugins, make sure you are using the latest version and try the solutions on the troubleshooting page. If you're unable to resolve your issue, post to the Zotero Forums.
See the word processor plugin changelog for version information.