Here is the official tutorial: https://github.com/qbittorrent/search-plugins/wiki/Install-search-plugins#steps-to-install-search-plugins-qbittorrent-version-3110-or-more-recent

In qBitorrent go to Search Plugins in the bottom right, then Install a New One. You'll go to that website link I posted and find a torrent site that has lots of content you like, like 1337, and click the little download icon off to the right of it in that table. That will open a tab with some computer code looking stuff. Copy this URL of the website and in qBittorent, in the Install a New One window, select web link and paste the link to the search engine plugin you chose. I did this for the top 10 or so most relevant looking websites for me in terms of language, content type, etc.

Now when I need a torrent I just go to my search plugin section of the program and type in the search terms I would normally use on Rarbg, and I find the movie I'm looking for.

Here is a YouTube video I found talking about the process:
https://youtu.be/nksLKqotTys