from web.config file with connection string who to interact 
means who to connect in 
gridview. in my system shows null something error what is 
the problem

The name of the default table adapter connection string 
looks something like the following: 
AppName.Settings.Default.ConnectionStringName

Naturally, AppName is the name of your application and 
ConnectionStringName is the name you've given to your 
connection string. This is the 'certain way' that Jay is 
talking about.

If you create a TableAdapter through the design time 
interface and configure the connection string to save into 
the config file, you can edit the config file and see 
exactly what connection string name is expected.