It's simple! Follow these 4 easy steps.

1. You need to create or copy an image in a new document on adobe. For example, I will be using a smaller version of a blend I made.
2. With the document open in adobe that you want as your brush, click edit > define brush preset.

4. Now if you open up a new document, click on your brush tool, right click and scroll down through your brushes, you will see your brush there ready to use.