Whether you're a professional artist or someone who just wants to doodle a bit, there is free software for you to try out there. It even might end up being your software of choice. If not, it might just be a great way of learning art and design without investing any money into it. So, here's some programs that I currently use or have used before.
1. MediBang Paint Pro
It's most reminiscent of Clip Studio Paint, it's just simpler. The interface is pretty easy to understand and get used to. The brush selection is limited when you first open the program up, but if you sign up for an account or login with your google you will get access to a bigger selection of brushes from the cloud. You've got your standard art program stuff like layers, line correction, tools like eyedrop, pen selection, shapes etc. For someone like me it's pretty much enough, I haven't found anything that I need that I couldn't find in MediBang.
2. Krita
Krita is another digital art program that is safe to assume as the reigning king of free digital art programs. Though honestly, I prefer MediBang nowadays. I used Krita for a while when I was still getting into digital art. It is very feature packed though the only downside for me was that some features for difficult to use. I'm mostly presenting this as an alternative to MediBang in case you don't like it.
3. PhotoScape
This is a free image editing program that I have used for a long time. Usually when I'm done drawing I will export my work and resize it, crop it, add text etc. using PhotoScape. You can create image pages that are useful for something like comics for example. I personally started using it for designing album covers for my teenage days bands.
4. Gimp
Gimp is probably the most well known free Photoshop alternative. I only used it a little bit cause I personally didn't like it. Mostly cause the interface is not the most intuitive. You can do most things you can do in Photoshop, it'll just be a bit more difficult.