If you put money in the bank, you get interest. If you borrow money from the bank, you have to pay the interest. You may pay the bank back in one payment, or you may make regular payments each month. Or you may be adding to your savings every month. Calgraph will do the calculations for each of these situations.
If you put money in the bank, you want to know what that money will be worth in the future.
This is Future Value.
If you know you will receive a sum of money in the future, it is helpful to know what it is worth now.
This is Present Value.
If you borrow money (perhaps to buy a car or a house) you probably will have to make payments every month until the debt is paid. This is a Present Value Annuity.
If you are putting money in the bank each month, you want to know how much you will accumulate in the future. This is an Ordinary Annuity.