Percentages are used everywhere, from calculating discounts to finding out profit margins and test scores.
Discount: A ₹1,000 shirt has a 20% discount. 20% of 1,000 is ₹200, so you pay ₹800.
Increase: You bought a stock for ₹1,000 and it is now worth ₹1,200. The profit is ₹200, which is exactly a 20% increase.