You use this.gridDataBoundGrid1.Selections.GetSelectedRows to get a GridRangeInfoList object holding any selected rows. Then you can iterate through this collection.
GridRangeInfoList ranges = this.grid.Selections.GetSelectedRows(true, false);
foreach(GridRangeInfo range in ranges)
{
for(int i = range.Top; i <= range.Bottom; ++i)
{
Console.WriteLine("row {0} selected", i);
}
}