First of all: a brush is a painting tool which texture is different htan the simple plain circle that comes in every drawing program. There's a lot of them: watercolor brushes, oil brushes, charcoal, pastel, pencil, pen, ink... each o them will help us achieve different textures. There's an intended use for every brush, but there's no probloem in using them in a different way.If you use FireAlpaca like me, you may want to find out a bit about "bitmap" brushes. Let's say you upload a black and white image: your computer will extract every black or dark pixel and make a brush out of that base. The opacity and flow can be modified later.
We can find these brushes on artist's packs, which are paid, or you can find them for free if you know where to look on the internet. Free brushes aren't as good as professional ones though.
Some programs even have the option of making your own brushes! It's a long process if you want it to turn out good. Personally I stick to those brushes i can find on google.
Soem artists do share their brushes for free like great artist Pheberoni,Some links:!
Paint Tool Sai
Photoshop
FireAlpaca
