It's a very simple system.
Remove the lid, then push down the clear brush guard and remove the rubber-band that comes on the brush. To get the brush started, press the brush down firmly on the back of your hand in a pumping movement to release the powder and you start to see it. It is useful to sweep your fingers across the top of the brush so when you see the little puff, it's ready to use. You only need to do this the first time you use the brush.
When you've finished applying your On The Go Mineral Powder, just pull up the clear brush guard and pop on the lid.
Click below for a short video tutorial.