Open source software has been mainly the only software I have used since I went to Ubuntu years ago. Unfortunately I am temporarily on windows, but not for long. On this page there will be links to sites that run amazing tutorials in Krita a fantastic free Open source software. If you own a graphic tablet or you draw straight onto a screen with a stylus Krita maybe what you are looking for.
Krita is available at https://krita.org To check it out before you download it there is a lot of good advice available at their site https://docs.krita.org/en/user_manual/getting_started/starting_krita.html A great starting point for beginners is https://docs.krita.org/en/
Concept Art Empire is another site with Krita tutorials This site is full of amazing tutorials for beginners or experienced users. Mostly video tutorials but really worth watching if you would like to learn Krita. https://conceptartempire.com/free-krita-tutorials/ https://conceptartempire.com/free-krita-brushes/
One well known artist, who generously over the years, has created tutorials for Krita, is David Revoy. I will post different pages of his work and tutorials to help with enthusiasm. On the links below you will find pages of tutorials.
https://www.davidrevoy.com/categorie3/tutorials-brushes-extras https://www.davidrevoy.com/categorie3/tutorials-brushes-extras/page2 https://www.davidrevoy.com/categorie3/tutorials-brushes-extras/page3 https://www.davidrevoy.com/categorie3/tutorials-brushes-extras/page4 https://www.davidrevoy.com/categorie3/tutorials-brushes-extras/page5 https://www.davidrevoy.com/categorie3/tutorials-brushes-extras/page6
Libre Graphics World is a great site covering more than one arts program. On their site you will find tutorials on Krita, Gimp, Inkscape and many other Open Source software packages. Because sometimes when starting a new program it is a daunting experience I tried to find as many tutorials form experienced artists. http://libregraphicsworld.org/ As with many sites I do not know how up to date it is.
GDQuest is another free tutorial site for 2D, 3D art https://www.gdquest.com/tutorial/art/krita-tutorial-for-game-artists/
Enjoy your journey into the free wonderful world of open source, where you can get involved, support, and have a good time, while you are learning.