This documentation was tested on a fresh Ubuntu Desktop 18.04.1 install.

Install the NetworkManager OpenVPN plugin if you don't have it. To do that, open Terminal and type:
sudo apt-get install network-manager-openvpn-gnome

• Generate and download an OpenVPN configuration file: My account > Services: VPN > "Generate OpenVPN configuration file" > "Generate"
• Open Settings and click on “Network”. Click on the + icon next to “VPN”.
• Choose “Import from file…”. Select the arethusa.ovpn file you just downloaded and click “Open”.
• In the “Identity” tab, enter your VPN username and password, then click “Add”.

Click on the Network icon in the status bar then “VPN” > “Connect” or “arethusa”.

Once connected, check your IP addresses.

The OpenVPN log is in /var/log/syslog , mixed with all other system logs. Skip until you see lines with openvpn.