I forgot to mention, if you're a fairly new coin collector, you REALLY need to get a loupe. You can pick one up for a bout $35, and it is the single most important tool you will have as a coin collector. If you don't know what a loupe is, it's essentially a small magnifying glass intended for use with coins. Most people like theirs between 7 and 10 power. Wizard Coin Supply sells them reasonably here: http://www.wizardcoinsupply.com/products/coin-tools/ If you join the American Numismatic Association, you get a discount with Wizard.
Here is a visual aid that will help you learn what to look for when trying to determine if you have a doubled die.