As you click the pen, serum will start to come out.
You may have to click a few times extra to start the serum (it may take up to 20 clicks during first use!).
The bristles will begin to look shiny when there is serum.
Holding the brush in the light will help you see where the serum is coming from and when it starts to come out.
Practice makes perfect and the more you use it, the easier it will be.