Hi!
The lifebars are divided in 3 sections: beginning section, mid section and end section.
The idea is to use to first use the beginning one, then fill with as many mids as you want and finish it with the end section.:
In this case I've used 1 beginning, 8 mids and 1 end to make a total of 10 hp points.
You can do the same with an empty one and then put one on top of the other, so you just have to cut a part of the one in the front to show the hp change:
I hope this helps you and thanks a lot for your purchase :)