In a few words, the app shows a series of screenshots with text and images indicating the steps you need to take. What you have to do is basically go to the official WhatsApp website, or to Uptodown, download the APK, and proceed with the installation. Additionally, Download Whatsapp on Tablet lets you watch a tutorial video, which easily shows you how to do this.
Download Whatsapp on Tablet is an app with a limited use. It only tells you how to download WhatsApp to your tablet correctly.