system.data.sqlclient class

sqlconnection con=new sqlconnction("your database connction string here")

sql command cmd=new sqlcommand("sql command,storeprocedure,con")

string cs="Server=[server_name];Database=[database_name];Trusted_Connection=true"; 
using(SqlConnection conn = new SqlConnection(cs))
{
   sqlcommand cmd=new sqlcommand("select *from emplyee",con)
   con.open();
   gridview.Datasource=cmd.ExecuteReder;
   Gridview.DataBind();
   con.close();
}