If you invest ₹10,000 and earn 10% in a year, you have ₹11,000. In the next year you earn 10% on ₹11,000, not just on the original ₹10,000. That extra ₹100 is the first step of compounding.
Over long periods the effect becomes dramatic because each year’s gain becomes part of the base for the next year. The two variables you control are (1) how long the money stays invested and (2) how regularly you add to it.
What you cannot control is the exact annual return. Markets move up and down. That is why illustrations on calculators always carry the note that past or assumed returns are not a promise of future results.