I'm assuming you mean drawing programs and the like. Lessee what we got!
I personally love Medibang. It's a free blessing from the heavens that is oriented toward digital linework and painting, if you can figure that out. Lots of tutorials and a supportive English fanbase. Most pixiv artists use it. Not exactly the best for photoshop-style editing.
I am not a user myself, but almost everybody I know uses FireAlpaca. Because of it's popularity, there's a ton of documentation.
Can't forget about Clip Studio Paint! It's good to look out for it, it goes on sale a lot. Tons of documentation and many interesting features.
As for posting art, I guess do some imgur magic? Or just upload through your pictures function in My Stuff, but that's quite limiting.