You can find old coin and paper money values in price guides. Unfortunately, figuring out exactly what your coins are worth is more complicated than simply looking the coin up in a price guide.
Country of Origin
Figure out what country distributed your old money. This information is generally written on the money itself.
Buy an up-to-date price guide for your old currency.
The denomination of your coin or paper money is how much it was worth when it was first printed. This info is also usually written on one of the faces of the money itself.
Many forms of money have been printed in multiple different types (i.e. Indian head pennies and Lincoln head pennies). The date on the coin should help you figure out what type of money you have.
The condition of your money has a great deal of impact on its overall value. The specific qualifications for certain conditions change depending on the type of money you are working with. Your price guide should tell you all about grading your old money.
The value in the price guide is an estimate based on market conditions at the time the guide was published.