How do i make a fall script?

I'm making a dam that's holds all the water and prevents the town from getting floods. im now asking you to make that for me so get that outta your head! what i am asking is to make a fall script. i want to make sure that when you fall from a great height you actually DIE! this might be asking to much. or it might be easy to make. i cant go on free models because either ill get lua virus. or its in-accurate because its from the old roblox studio. if this is breaking the rules by asking for someone to teach me to make it. you can remove it. because, its just a random question anyway. but please! help me with this!