To learn about coins and their values, your best bet is to research by joining the American Numismatic Association. You can also check out the U. S. mint's home page or a website like Coin Today or Coin World. You can look up your coins in the "Guidebook of U. S. Coins" also known as the Red Book.
If you are referring to a Franklin Mint coin, you can check values on the online auction or sales sites. Look for sold prices.
The most valuable coins are old coins in mint condition. Demand and scarcity effect value as well. Places like Franklin Mint who mass produce items for some supposed investment create an illusion of interest but the vast numbers produced devalue the products.