classes in asp.net using c#

Generally we don't use class to write any sql commands or statements but here's how u can create a class with a connection string:

public class connection
   {
       public static  SqlConnection getconnection()
       {
           SqlConnection con = new SqlConnection(@"server=servername; initial catalog=databasename; User Id=username; Password=password;");
           return con;
       }
   }

here's how to use that connection for retrieving data

 public partial class _default : System.Web.UI.Page
    {
protected void Page_Load(object sender, EventArgs e)
        {
            SqlConnection conn = connection.getconnection();
            conn.Open();
            SqlDataAdapter da = new SqlDataAdapter("select * from tablename", conn);

            DataSet ds = new DataSet();

            da.Fill(ds,"tablename");
            GridView1.DataSource = ds;
            GridView1.DataBind();
            conn.Close();

        }
}

happy coding :)