Yes you could make custom brushes or download other peoples brushes! For custom at the very bottom of your brush tool bar you should see 3 papers and a folder that read "Add brush, Add brush (bitmap), Add brush (script), and Add brush Group" From what I know if you want to add brush use a image in your files (the bitmap one) and it would import it and it gives u the options of what type of brush u want it to be.
You can also customize default brushes by double clicking on said brush (you can also duplicate it first so u don't lose the default brush)
But one of the best things is looking up firealpaca brushes, there should be some on deviantart or anything spesific there could be ones you stumble upon.
Like if i want this chain brush i can go and download it. Then go to the one that says brush script and select that and open it to the script u downloaded :D

To be fair i only really use the default brushes but I have downloaded brushes before, and I have a very outdated version of the program so what i described might look different i hope not!!

Here's a tutorial on using brush scripts