public class GroupDescription 

private void Form1_Load(object sender, EventArgs e)
{
            _flex = new C1FlexGrid();
            _flex.Bounds = new System.Drawing.Rectangle(20, 80, 750, 550);
            this.Controls.Add(_flex);
            OleDbConnection con = new OleDbConnection("provider=microsoft.jet.oledb.4.0;Data Source=" + Environment.GetFolderPath(Environment.SpecialFolder.Personal) + "\\ComponentOne Samples\\Common\\C1NWind.mdb");
            DataTable ordersTable = new DataTable();
            new OleDbDataAdapter("Select * from Orders", con).Fill(ordersTable);
            _flex.DataSource = ordersTable;

            for (int column = _flex.Cols.Fixed; column < _flex.Cols.Count; column++)
            {
                grpByCombo.Items.Add(_flex.Cols[column].Name);
            }           
            grpByCombo.SelectedIndexChanged += GrpByCombo_SelectedIndexChanged;
            grpByCombo.SelectedItem = "ShipCountry";

            //Hide the grouped column (Optional)
            _flex.HideGroupedColumns = true;
}

private void GrpByCombo_SelectedIndexChanged(object sender, EventArgs e)
{
            //setting the grid's GroupDescription property
            _flex.GroupDescriptions = new GroupDescription[] { new GroupDescription(grpByCombo.SelectedItem.ToString(),System.ComponentModel.ListSortDirection.Ascending, true) };
}