You should now have the tools you need to create great digital artwork. A good tool is not a substitute for artistic training and practice though. Improving as an artist is a lifelong journey. There will always be people better than you and others that are worse. All that you can do is take one step at a time. An application like Krita is just one piece of the puzzle.
I hope you have found this book helpful. I have learned a lot myself and have grown throughout the process. I look forward to seeing your artwork in the future.
Artwork by Cesar