Check out a tutorial by Wiktor Öhman that explains the process of importing custom brushes and sculpting inside Mixer.
Learn how to import custom brushes and sculpt in Quixel Mixer in this short tutorial with Wiktor Öhman.
Quixel Mixer (Beta) – is out NOW!
For more on Quixel Mixer, visit this page.
Quixel
You can find a detailed breakdown of the tool by Quixel here.