The way the app works is very simple; while you're having a conversation on Whatsapp, press the 'attach an image' button and instead of selecting one from your gallery, you select Paint for Whatsapp. Whereupon the app will open up and you can start drawing.
Paint for Whatsapp comes with very few drawing tool options. Basically, all you can do is draw using your fingertip and select the color you want to draw with. That's it. When you finish your drawing, you save it to your phone's memory and then automatically send it to your Whatsapp contact.
Paint for Whatsapp is a small and simple tool with which you'll be able to do drawings and send them via Whatsapp in just a few seconds.
Requires Android 1.5 or above.