Compounding means the returns you earn start earning their own returns. Year 1's profit becomes part of Year 2's investment, which earns more, which becomes Year 3's base — and so on.
₹1,000/month invested for 30 years at a 12% annual return becomes about ₹35 lakh. Of that, only ₹3.6 lakh is what you put in. The remaining ₹31+ lakh is compounding doing its thing.
The three inputs that matter: how much you invest, what return you get, and how long you leave it alone. Time is the most powerful of the three — you can't buy it back.
Analogy: rolling a snowball down a snowy hill. It starts fist-sized and boring. By the bottom, it's the size of a car. That's compounding.