How to add database file in c# project folder?

Question

Hello
I use VS2010. I created a database in SQL exapress 2008(installed with VS2010). when I want to add data to database it works fine. But when I add the database file in Project (By add existing item), the inserted data does not save in database.the data is only available until the program is running. (when I Close the program and start it again the inserted data does not exist)

Any one knows what the problem is with this program?

thanks