In simpler terms, to calculate which things we can afford if our salaries remain the same in the same country where I want to buy things.
Let me clear your confusion by presenting you with an example here how it goes, Imagine you have a ₹ 10,000 salary, you want to move abroad to the United States of America, should you directly convert your currency to check how much you should be paid ?

Well actually No, let's check with a burger, check if the price of 🍔Burger is the same in the United States of America as you have right now in India. Even if you have tried to convert the price of it, you will find it slightly expensive or affordable so are you convinced now why exchange rates are not correct to check your salary.