There is a script which you can use to easy install an openvpn server.
Here is how to use the config in the network-manager: convert_openvpn_ovpn_files_for_use_in_network_manager_chrisjrob.pdf
And here how to config an static IP:
Still I only added this:
ifconfig-push 10.8.0.100 255.255.255.0
Remind that: You need to enable the TUN/TAP and the PPP on your server. This is from RamNode configuration panel: