To make it happen, follow these steps:
- Update Whatsapp to the latest version on your mobile device.
- Go to https://web.whatsapp.com/. The page should display a QR code.
- Open whatsapp on your mobile and select 'Whatsapp Web' (see image below) and scan the QR code on your PC. You don't need any other scanning software to do this - it's done within the Whatsapp interface on your mobile.
- Do the same for other devices - eg your tablet, laptop etc...
It's free to use for year 1 and then costs $0.99 per annum (currently). You can download it here.