Money is one of the earliest abstract systems a child runs into and one of the last ones anybody explains. They handle coins at four and get a real explanation at twenty-four, usually from someone selling them something.
The concepts here are deliberately ordered. Value and trade come before money. Money comes before saving. Saving comes before investing. Skip a rung and the idea above it turns into a rule to memorize instead of something to understand.
Money is a way to trade what you have for what you want, without carrying a goat around.
Money is a way to trade what you have for what you want without needing to find one person who has both. That is the problem it was invented to solve.
Investing is using something valuable now, hoping it becomes more valuable later.
Investing is using something valuable today because you think it will be worth more later. Sometimes you are right. Sometimes you are not, and that part is not optional.