iOS is a mobile operating system developed by Apple Inc.. It is the operating system that powers many mobile devices, including iPhone, iPads and iPod Touch. It was unveiled in 2007 for the first-generation iPhone, but has been since extended to support other Apple devices such as the iPod Touch (September 2007-mid-2022) and the iPad.
First thing you need to do is go to the Apple App store on your chosen device (iPhone, iPad), find and download an app for the VPN provider you have chosen, then sign up for the service and create an account with the VPN provider.
Once you have pain for the plan and created an account do the following:
Make sure you have VPN switched off when not needed, as it does use up extra data (if you are on a limited plan).