SearX is a metasearch engine. That means it returns results from other selected search engines. It's accessible via an onion address and provides a private search ability. Really the only advantage it gives you over searching directly from a Tor browser is the ability to customise your search experience.
In terms of security both the connection between you and the server, and the outgoing connection from the server to other search engines are onion routed. This should give you a reasonable level of search privacy.
Once it has installed go to *About* on the *Administrator control panel* and look for *searx*. Take a note of the onion address, and you can then enter that into a Tor compatible browser.
In a Tor browser click on the magnifying glass icon next to the search box and you can then add your metasearch site. A small icon will appear called "/Freedombone Metasearch/" and you can then right click on it and make it the default search.
It's possible that you might not want just anyone on the interwebs to be able to use your metasearch engine. Even with the onion routing this might carry some legal risk or make you a target for denial-of-service attempts (although Tor's rate limits and the firewall will give you some defense against that).
To enable password login go to the *Administrator control panel* then *App settings* then select *searx* and *Enable login*. If you select "yes" then the password will be displayed.