Vilfo has several pre-configured VPN providers to choose from. If you use a VPN provider that is not pre-configured in Vilfo, you can still connect to their servers as long as they support OpenVPN.
You can add your VPN provider by going to the tab VPN Providers and then by clicking on Add custom provider. You'll be able to upload their OpenVPN configuration files.
Please note that Vilfo currently only supports VPN servers that use credential based authentication and not key based authentication.