NEED HELP PLEASE to make zombies attack player and lower his health!

[puzzlemenow]

hi, i am trying to make a game where at one point you will encounter zombies and skeletons. i want the player to be able to kill them. however at the same time i need help on how to make the zombies/skeletons attack the player and when they do hit the player, lower his health bar.

thanks so much!

here is my game if u need to look at it.