To download WhatsApp on your device go to the website www.whatsapp.com.
Then go to the download tab located in the top navigation bar.
Now you are on the download page. WhatsApp site has mentioned information about supported devices. Choose the appropriate device and click to download. for instance, mac user will select the Mac OS.
Once you decide the device, click on the link to begin the download. The WhatsApp app is a lightweight application which will be downloaded immediately.
Once the download is complete, double-click on the application to run the app. Now install the app as you do it for other software. Read the structure shown in the application window. Just a few more clicks and you are fully setups for using WhatsApp app on your device.
On Mobile devices, WhatsApp will ask you to verify your mobile number so follow the instruction carefully.