There are several downloads available from the App Store that allow your iPad or iPhone to function as a second monitor. These work wirelessly and will only function if you have a Wi-Fi network.
All are simple to use and setup, but there is a small cost involved. At the time of writing, this ranges from £2.99 to £5.99. The software can be purchased from the App Store and will guide you through the setup process. You may also need to download a small file for your PC or Mac to get everything up and running.
Please check the app description and the developer’s website before purchasing the software to ensure it is compatible with your system.
Air Display: http://avatron.com/apps