Yeah, you'll need to unwrap your mesh first (the shader gizmo was already unwrapped for this lesson) and you can create custom materials for your mesh either in Blender (using 2D or 3D texture painting, discussed in previous lessons) or after exporting your unwrapped UV map, you can paint in an external program of your choosing (Photoshop, Krita, Gimp, etc)
Hope that helps!