Urgent help with Health System in a 2D game

I have a very specific question to ask, I’m working on a health system for a group project but I’m very inexperienced in scripting. Using C# I have to create a health system that also acts as a score system-
If an enemy attacks the player, the player loses score points; when the score reaches 0 its a game over.
When a player attacks the enemy they gain health points/score, after reaching certain amounts of points the player goes to another level.

specific info:
player base health 50
enemy damage 25/30
player attack damage 50
enemy health 100
score gain 10/20

The Level System in this series should get you a head start: