i'll give you an example how qvpn can be used.
with qvpn i can add my privateinternetaccess vpn subscription account to it, using the openvpn file ovpn to qvpn. when thats added and logged in, you can then either
1. make the qvpn active vpn your default active gateway. meaning all internet traffic on the qnap is routed through your vpn connection
2. DO NOT make it the gateway. meaning that you have vpn running, but it's not routing your qnap traffic through vpn. So you would instead go to appcenter, then for the download station, there is a pulldown menu where you can then select to use the QVPN to route your traffic only for that app, or any other apps that you setup in this way.
That is how it works.
PIA is a subscription based VPN, with their servers located in many different countries. the purpose is, i use their internet via a tunnel, so that my isp does not know what i am using my broadband for since it's encrypted. It also provides me a foreign ip address. So that is how it works.
So the PIA VPN in qvpn would be added under the VPN client settings.
I guess if you had 2 qnaps, one of which is offsite and setup with a QVPN server vpn. You can then login to that via qvpn, and gain a similar benefit. This is fine for like a secure connection to your offsite vpn, if that is the intent for your usage for vpn.
But seeing as you are planning on using downloadstation with vpn, then i guess your intent is downloading anonymity? i would then suggested just getting a vpn subscription which has MANY many servers. I would suggest surkshark
anyhow, once you get your vpn setup you can test that it works by
1. check virtual network, confirm your ip. This is only IF you are using QVPN as the default gateway, if not do step 2.
2. go to ipleak, download the torrent magnet with download station. then check the ip whether it is using the VPN or your real ip
Make sure in virtual network for your qnap that you disable ipv6. i find that enabling that tends to leak out your real ip. best to disable.