i am developing an application in C#,i have create database1.mdf by
right clicking on my project,add item
then creating a database.
my intial problem was,i was able to execute query correctly but those modification wasn't reflected in main database
finally after lot of surfing i changed copy to output directory to copy if newer but still i am not able to rectify my problem.

now i am feeling that i need to connect to sqlserver using connectionstring but i don't know username,servername,password etc...

can anyone help me please

Have you figured this out yet? You seem to have quite a few things to research but if you still need some help just say.

Do you mean you don't know how the connection string looks or you don't know the credentials to the database? Because we don't know them either...
If you have SQL Server management Studio or something similar installed you should be able to get the server name easily enough (it'll show in the list of databases).
If you set up the SQL database didn't you set up credentials at the time?