Where does the interest in compound interest come from? And how do you take advantage of it?

BLOOMBERG (December 16, 2021) — In my head, interest is reinvesting the money made on an initial deposit. But for example if I buy one share of VTI and it grows 10% by next year and I contribute $100 per week, that’s not an example of compound interest, is it? I guess at the end of the day I’m not totally sure how to take advantage of compound interest. What am I missing here?