How are vpn services created?

Question

openvpn

I would like to know how vpn services are created, for example, like this one https://www.privatetunnel.com/ .
1) Do they write their own server software or use an openvpn server?
2) If you use openvpn, how can you configure access to vpn servers by login and password?
3) Is it profitable if you put vpn servers on vps?

Answer 1

1) Do they write their own server software or use an openvpn server?

Not why.
In addition to billing, it is expedient and independent.
In addition to OpenVPN, there are plenty of others. For example Strongswan.
3) Is it profitable if you put vpn servers on vps?
This is not a technical issue.
You first recruit somewhere so many customers so that you pay off ...