I am create one application using c# and Sql server.
suppose database stored on one machine how to access this database to another machine,
i.e database which is created using sql server stored on one machine and application run on another machine how to access this database which are stored on another machine

You need to configure your SQL Server instance to allow remote connections. The msdn page is for sql server 2005, if you are running a different version, eithe rlet me know which or google for "remote connection" for your version.

Then in your Conneciton string your dfatasource will be "Data Source=[PCNAME]\[SQL INSTANCE NAME]" so mine would be "Data Source=RYSHAD-PC\SQLEXPRESS".