There are many ways to determine the value of a stamp collecting hobby. There could either be sentimental or monetary value. The value of stamps can vary greatly. It is usually based on what year the stamp was originally manufactured in or the value can be determined by the rarity of the stamp.
Well you can determine the value of your stamps. If your stamps are over 100 years old they will be worth more to people who collect them all over the world. And because of that you can list them on ebay and have people bid on them and make a lot of money.