Of course, this version of WhatsApp works in much the same way as the versions you would have already seen on iOS, Android, and Windows Phone, as well as older versions of BlackBerry. It connects with your existing contact list, matching up those phone numbers with the directory of people who have WhatsApp. From there, you can engage in group chats, send texts, share pictures, and more.
The BlackBerry 10 version in particular has been coded to integrate with BlackBerry Hub and Flow, so you can check your WhatsApp messages without really having to dig into the app itself. You can pick it up as a free download in BlackBerry World.