Script Detecting Actions?

[FireHeaven]

I'm kinda new about scripting as I haven't done much with them. I understand a lot of the basics... I was wondering, is there anyway to detect an action being taken? For example, pressing a button executes a script that doesn't interfere with the command that button is assigned too?

 

Is there a variable that detects when the player reaches 0 hp?

 

Can you make a script that when the user presses a button it does a random action you assigned to it?

 

Thanks in advance!