1. From one of NordVPN's official .ovpn files (nordvpn.com/ovpn), create the two following:

ca.crt: containing this part of the .ovpn file:

-----BEGIN CERTIFICATE-----
(...)
-----END CERTIFICATE-----

TSL.key: containing this part of the .ovpn file:

-----BEGIN OpenVPN Static key V1-----
(...)
-----END OpenVPN Static key V1-----

Save both ca.crt and TSL.key in a known directory.

2. Open VPN editor app. Add new connection, and set it up this way:

ID: AnyNameToRecognizeTheConnection
Remote: x.x.x.x:1194
(choose the IP of any NordVPN server)
Type: Password
Username: xxxxxxxx (provided in your user's account)
Password: ·············· (provided in your user's account)
CA certificate: ca.crt (file previously created from the .ovpn)

Advanced:

Tick "Use renegotiation interval: 0"
Tick "Use LZO data compression
Tick "Use custom virtual device type:"
TUN
and name: tun

Tick "Use custom tunnel MTU: 1500"
Tick "Randomize remote hosts"

Security:

Cipher: AES-256-CBC
HMAC authentication: SHA-512

TLS:

Tick "Verify peer certificate"
Peer certificate TLS type: Server
Tick "Use additional TLS authentication:"
Key file: TLS.key (file previously created from the .ovpn)
Key direction: 1

3. The connection is ready to use. Turn the switch on and wait for it to go green.
   Try ipleak.net from a web browser to test the connection.