I couldn't find the advantages and disadvantages of using a database over plain files. Would you please help me?
A few database advantages:
Plain text doesn't have much except for the most dead-simple application
Basically, if you are doing anything other than the most simple data manipulation (especially if you ever expect to have concurrent modifications, complex relations, multiple users, or even just a lot of data) it's well worth getting used to using a database. PostgreSQL is my favorite, although I'm sure you'll find conflicting views on that one :)