MySQL is free and quite powerful.
You will need to learn how to design and build a database if you want good performance when it gets huge. At smaller sizes, anything will be ok. You will need to learn how to perform SQL tasks like queries and merges, which is pretty easy. I think there is a for Dummies book on SQL. For the database knowledge I would recommend you go to
https://www.mysql.com/ which has a developer zone with forums and all kinds of goodies to get your going.
