What happens next?

How to draw on snapchat
Take your snap as you normally would.
You can draw on both photo and video snaps. When drawing on a video snap, the drawing will stay on top of the entire video.
You may want to consider taking the snap on an ipad or android tablet if you have access to one. The large screen on these devices will allow you to draw with much more detail than on your phone, and will look very sharp when viewed on devices with smaller screens.