Setting up connection with Synology NAS

[Kurzwallen]

Dear all,
My question may seem stupid: I'm a newbie in the world of VPN. I'm trying to find out how I can connect from Germany with my Synology NAS 418J located in Brussels. Sometimes the terminology used in the documentation is pretty confusing...

My 'infrastructure'
Desktop running under Windows 7 (soon Ubuntu Bionic Beaver)
NAS (in Brussels) is connected to a VDSL-modem/router.
VPN-server on NAS is installed. IP-reach: 10.8.0.0. - 10.8.0.255
Protocol: TCP
Coding: BF - CBC
Verification: SHA512

I can log in on my NAS (as admin) from Germany, via the DDNS of Synology. But further... I thought I understood it... but sorry, right now I don't understand it anymore...