A VPN (Virtual Private Network) is a protocol that allows you to send and receive data across a public network (e.g., the Internet) without being detected or exposed to any threats. 

A VPN can be used to protect yourself when accessing content that is not available in your region, and also to mask your IP address and location. This is useful for accessing websites and services that are blocked or restricted in your region.

To use the VPN Client Pro app, you will first need to download it from Google Play. Next, you will need to install it on your Android device. After that, you can start using it. To do so, open the app and click on the "Connect" button. This will connect you to the VPN server. After that, you will be able to see the VPN server name and your device name.

To connect to a VPN server, you will need to select the desired server. You will also need to choose the protocol that you want to use.