Just use this like you would a normal brush.
If you hold it like you would a pencil and at an angle almost 90 degrees to your work,
just using the tip of the brush you will get lots of very fine strokes from one load of paint.
Once you’ve finished using it, Clean the brush with distilled water.
Rinse the bristle tip thoroughly and carefully,
roll the bristles on a surface to bring all the bristles to a point like you do other brushes.
I’ve had mine for a couple of years and I still use it now"
The paint I use is too thick to put in the pen. Also, with it being trimmed, if you put paint in them, you have to disassemble to clean. The bristles never go back in correctly. Just wash them without taking them apart and they will last years if taken care of properly.