[Begginer]How do I call a function when an actor is hit.

Hi, I am new to the unreal engine with C++. I have a new actor class with the FPS template. I have created a damage integer property with a default of 100. How do I with c++ take away damage when I shoot it or when it collides with something. I am unable to find a proper tutorial. If you could show me or point one out that would be great.
Please forgive me for any mistakes as I am new to this forum.

Here you have ^^: