The Rule of 72 is a helpful tool that you can use to approximate when money doubles, interest rate it must earn to double, and how many times it doubles during a set period of time. Which you can use to calculate money from investments or how much money you will owe after a certain period of time.
Compounding Interest is the interest earned on interest. You will want compounding interest over simple because you will make more over time/ in the long run.
After I started investing at the age of 12, I quickly found out just how much compounding interest can benefit me in the future, like today, I have $100,000 dollars in my bank account!