The paintbrush tool allows you to copy a material on a piece of geometry and apply it to any number of other pieces of geometry.

1. Click on the dropper pipette button.
   
2. Click on the piece of geometry you would like to copy.
3. Click on the paintbrush button.
   
4. Click on any number of geometry pieces to apply the copied material to them.

When you have finished using the paintbrush tool, click the paintbrush button again to stop using it.