Clip Studio Paint exists on The mobile version operates on a subscription ($4.49/month). However, you can use it for free up to 1 hour per day.
Certain hardware manufacturers partner with Celsys to include extended free versions of Clip Studio Paint with your purchase.
One of the best things about CSP is the community. Even on the free trial, you can download thousands of free brushes, 3D models, textures, and screentones from the Clip Studio Assets store.