Get yourself a "Whitmans Red Book" it is a great guide in telling you what you may have. Key dated coins are usually going to be coins with the least amount of mintage. for example a 1909 V.D.B. "S" penny is considered a key date coin the mintage on this coin was 484,000 while a 1909 V.D.B. no mint mark was much more common with a mintage of 27,995,000 a good coin book will be able to tell you a lot about what is key and what is common. note that the above two coins are very similar but that little "S" mint mark is a difference of hundreds if not thousands of dollars depending on grade. Hope this answers your question. Good luck