To use these brushes, you will need:

The iPad app Procreate (the brushes will only work in Procreate)

An iPad + stylus: even though the brushes will work with other iPad models and third party styluses, I recommend the iPad Pro + Apple Pencil combo, as they're currently the most precise & accurate tools for drawing in Procreate. The brushes were created & tested using an Apple Pencil so I cannot guarantee that they will behave as advertised with third party styluses.