I wanted to share my way of doing a HP bar, you can experiment alot to get a nice HP bar, this tutorial just shows some basics and the easy way of creating one.
First, create 3 sprites, called BarRED,barGREEN & PLR . Fill the redbar with red color and the green with green etc.
Now the pin behavior i have just added if you want it attached to the player, if the player is moving, this you can skip.
Add the keyboard plugin for your project, also set 2 instance variables on either the PLR or barGREEN sprite. 1 instance var called CURHP and 1 called MAXHP
then, add a event, on KEYBOARD KEY PRESSED X substract 10 from curhp, set the redbar width to the instance variable MAXHP.
Add every tick > set width of greenbar to object.curhp
I set the bars to be containers with eachother, wich means if 1 is created, the other 1 is created to, if 1 is deleted, the other one is deleted to.
I did this tutorial for a friend very fast, if u need help just ask.