The ContentExample project might seem difficult, but its actually fairly straight forward once you realise how things are connected. All you need to look at is the HUD blueprint and the health bar material.
The material does most of the hard work; it basically draws your health bar from the maximum health with one texture, then colours in a percentage of it with the second texture, based on your current health. All you need to do then is let the health bar know your current health. I don’t have Unreal to hand, but I found this shot that basically shows you how to do that.
In here, its calling a function from your character blueprint to get the player’s current health (for testing purposes, you could just get a float/integer variable and set it to a random value below your max health). The important bit is the scale parameter and making sure that the parameter name matches the name in your material. This will tell your health bar how much health you currently have and thus give you your working health bar.
Taking damage is something else that you would set up to impact your health value in the character blueprint.