I agree with aquarium - my advice is to pick a database, get yourself a good beginners book for that database, and read. MySQL is a good database, and Paul Dubois wrote a good intro book called "MySQL", and I think there may(?) be a 2nd edition out but not sure about that. I learned MySQL using Paul's book - excellent book that takes you through the whole thing, including MySQL setup and authentication, and gives you an SQL primer too. The book pretty much assumes you are a database beginner.

HTH.