I won't go into details with math, I will just teach you the basics of it. You can use math for 2 purposes, addition or subtraction. Here is an example of each:

local x -= 1

local y +=1

game.ReplicatedStorage.NumberValue1.Value = x

game.ReplicatedStorage.NumberValue2.Value = y

This will subtract 1 from NumberValue1 and add 1 to NumberValue2.