The page you are currently looking at offers your web browsers a search plugin for DuckDuckGo via Tor (.onion). How this is visualized or available to you depends on your web browsers and your settings.
The following picture shows how this may look like in Firefox (desktop version) if you have a dedicated search bar (i.e. not combined with the URL bar).
The direct link to the OpenSearch plugin is here: ddg-via-tor-opensearch.xml