private string GetConnectionString(){
        //call the Connection string that was set up from the web.config file
        return System.Configuration.ConfigurationManager.ConnectionStrings["YourConnectionStringName"].ConnectionString;
}

private void BindGrid(string startDate, string endDate){

        DateTime dStartDate;
        DateTime dEndDate;
        DataTable dt = new DataTable();

        //Check if the string has the valid date format
        if (datetime.TryParse(startDate, out dStartDate) && datetime.TryParse(endDate, out dEndDate))
        {
            SqlConnection connection = new SqlConnection(GetConnectionString());
            try
            {
                connection.Open();
                string sqlStatement = "SELECT <ColumnName> FROM <TableName> WHERE DateColumnName > @DateFrom AND DateColumnName < @DateTo";
                SqlCommand sqlCmd = new SqlCommand(sqlStatement, connection);
                sqlCmd.Parameters.AddWithValue("@DateFrom", dStartDate);
                sqlCmd.Parameters.AddWithValue("@DateTo", dEndDate);
                SqlDataAdapter sqlDa = new SqlDataAdapter(sqlCmd);
                sqlDa.Fill(dt);

                if (dt.Rows.Count > 0)
                {
                    GridView1.DataSource = dt;
                    GridView1.DataBind();
                }
                else
                {
                    //Show no Records found
                }
            }
            catch (System.Data.SqlClient.SqlException ex)
            {
                string msg = "Fetch Error:";
                msg += ex.Message;
                throw new Exception(msg);
            }
            finally
            {
                connection.Close();
            }
        }
}

protected void Button1_Click(object sender, EventArgs e)
{
    BindGrid(TextDateFrom.Text, TextDateTo.Text);
}