1. Update your system

First, run the apt command to apply security updates:

sudo apt update
sudo apt upgrade

2. Download and run openvpn-install.sh script

DOwnload installation script using short url as follow and update chmod :

wget https://git.io/vpn -O openvpn-ubuntu-install.sh
chmod -v +x openvpn-ubuntu-install.sh
sudo ./openvpn-ubuntu-install.sh

Select UDP (recomendded), Port default, DNS use 1.1.1.1 or Google, client name, just give some name for example client-vpn, then openvpn will generate file client-vpn.ovpn in the /root directory

3. Check status, start, stop or restart service

sudo systemctl status openvpn-server@server.service
sudo systemctl start openvpn-server@server.service
sudo systemctl stop openvpn-server@server.service
sudo systemctl restart openvpn-server@server.service

4. Using opvn file

On Windows, install OpenVPN GUI and load client-vpn.ovpn file. From taskbar, right click OpenVPN icon and select appropriate vpn and click connect. OpenVPN will generate private/local IP addresses such as 10.8.0.1/32

5. Test/Verify connection

ping 10.8.0.1 #Ping to the OpenVPN server gateway
ip route #Make sure routing setup working
## the following must return public IP address of OpenVPN server ##
dig TXT +short o-o.myaddr.l.google.com @ns1.google.com

6. Add or remove a new VPN user with a certificate

You need to run the same script again for adding or removing a new VPN user to TLS certificate. For instance:

$ sudo ./openvpn-ubuntu-install.sh

This is summary from Ubuntu 20.04 LTS Set Up OpenVPN Server In 5 Minutes