You can use Whatsapp on your Smartphone but also on a Android-tablet, iPad or iPod. You can also use Whatsapp online.
You can use the online version of Whatsapp by web.whatsapp.com , scan the QR-code and then the authentication takes place. You can view your chats and send new messages. You have almost all the options, you can even take photos with your webcam.
To use Whatsapp online your phone should also be connected to mobile internet.