It takes some time to figure out, but basically you need to:
Install docker and docker-compose
Install portainer (optional, but my recommendation. Its docker app that provides simple GUI to manage all other docker containers)
Create docker-compose with configuration for qbit and gluetun, then load it in portainer using stacks (look for examples on google or aks again when you get to this part)
Done
Alternative is just setting VPN in your existing qbittorrent. Never tried that, but you should set everything using qbittorrent settings I suppose