Find yourself a copy of the Guidebook to United States Coins. It is published annually, but for your initial purposes, a several-year-old copy will do just fine. They can often be found on the cheap at thrift stores, used book stores, or online. It is commonly called the "Red Book" and has a wealth of information regarding the history of US coinage, mintages (which is a large factor in determining value - and it doesn't change over time), plus descriptions of what you are looking at: where to find mintmarks, varieties, grading, etc. Then, if you have a coin for which you really want to find a value, you will be educated on what you have and will then be able to do a better online search.
John in ID