Just tap the icon labeled WhatsApp Web within this apps menu bar.
Just like the web browser version, you have to sync this program with your cellphone by scanning a QR code which you'll be able to do from within Whatsapp on your smartphone. Luckily, this totally independent desktop client version is easy to run within its own window, and has all the features of the Web version. One of the biggest issues with WhatsApp web is that to use it on your PC you'll need to run a compatible browser.
