To draw and paint directly with digital tools is not easy in fact. One thing that I recommend is to drawing first in the paper, then bring this art to the digital using a scanner or even taking a photo with a phone or tablet and do just the painting in the digital. Also the tools are very important when you're doing digital art. They don't need to be fancy or expensive, but they must have the basic features. So if you're using a PC/Mac and Photoshop or a similar software like Krita, you'll need a tablet with a good pen that reads the amount of pressure and angle of the pen on the surface. Good models without screen are the Wacom Bamboo or Wacom Intuos. Wacom with screen are very expensive, so if you want a model with a screen I really recommend the Huion models. This brand has a very good quality and the price is very affordable. If you're using an Ipad or an android model you still can do the same: take a photo from your drawing and start to paint digitally using a good app made for painting. The idea is: take the photo or scan your drawing, bring it to the software or app that you're using, transform the image in a layer and set the blending mode to multiply. Then start to paint in another layer under this drawing. You can create different layers to do different things or paint everything in a single layer, your choice! I hope it helps you! :)