The tutorials I have come across usually let you create a dababase from scratch creating a .mdf file or something and so on. However, what if I already have a SQL Server Express set up with the needed database? How do I tell my model to use that database?

Right now, all my model contains is basically some classes that execute stored procedure on my own database and return manupulated data. Should I leave it as it is? What are the benefits of going through the full-fledged model approach that tutorials demonstrate?