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