Also, if you need to know how to get an orderid, just get a dataset of orders and then set your where clause so that you could get the orders that you want based on your criteria.

DataSet dsOrders = OrderInfoProvider.GetOrders(siteid) // Note: this method has multiple signatures, so you an also call it like this OrderInfoProvider.GetOrders(string where, string orderby,int topn, int siteid);