Adobe Photoshop is by far the most popular software for painting. But even with a mountain of free tutorials and guidance on painting in Photoshop, you may still feel a bit off. More practice helps but sometimes you might want to try some new brushes too. Digital artists across the world release their brush sets online.
40+ Photoshop Brushes For Artists: Best Drawing & Painting Brush Packs
Cartoon Brush Vectors, Photos and PSD files | Free Download