What are animated brushes?

[shellyhoward]

(01-02-2019, 10:56 PM)Ofnuts Wrote: Same as plain brushes:

• if the brush is grayscale (Image>Mode>Grayscale) then it is used as a mask, the white is transparent and the black assumes the current paint color,
  
• if the brush is RGB (Image>Mode>RGB) then it is used as is, the shape of the brush being determined by the transparent pixels
  

When I create a New Image then, I should choose Grayscale?  And what about the Fill With section on Advanced Options?  Do I put Background Color or Transparency or what?  

Also, when I make the new layers for this animated brush, do I copy the previous layer, or just add a new layer? Or does it matter which I do?