It is a very broad topic, you didn't specify what kind of a drawing program you'd want to make. If it's a simple raster drawing, like mspaint used to be, it is not that complicated to make. But complexity quickly adds up - filters, transforms, brushes, layers - it grows in complexity quickly. The easiest GUI in rust I found so far is egui. It provides an immediate mode for drawing graphics that is really simple to grasp very quickly. If it is the best in the long run is questionable, but to get your feet wet - I'd say is perfect