The Pattern Stamp Tool paints with defined pattern:
In the Toolbox, select the Pattern Stamp Tool.
Set brush size and hardness*.
Define pattern.
Paint.
on the Options bar, define blending mode (in the movie, the author selects "Mutiply")
and "Opacity".
The Aligned gadget on the Options bar (not selected by default) forces the starting point to follow
your mouse, even after you complete a stroke, while leaving it
off starts the starting point back to it's original location at
the start of each stroke.
Tool paints with defined pattern: