Study the OrderSelect() function. Get to know it well, it is important.


bool OrderSelect( int index, int select, int pool=MODE_TRADES)
The function selects an order for further processing. It returns TRUE if the function succeeds. It returns FALSE if the function fails. To get the error information, one has to call the GetLastError() function.
The pool parameter is ignored if the order is selected by the ticket number. The ticket number is a unique order identifier. To find out from what list the order has been selected, its close time must be analyzed. If the order close time equals to 0, the order is open or pending and taken from the terminal open positions list. One can distinguish an open position from a pending order by the order type. If the order close time does not equal to 0, the order is a closed order or a deleted pending order and was selected from the terminal history. They also differ from each other by their order types.
Parameters:
index - Order index or order ticket depending on the second parameter.
select - Selecting flags. It can be any of the following values:
SELECT_BY_POS - index in the order pool,
SELECT_BY_TICKET - index is order ticket.
pool - Optional order pool index. Used when the selected parameter is SELECT_BY_POS. It can be any of the following values:
MODE_TRADES (default)- order selected from trading pool(opened and pending orders),
MODE_HISTORY - order selected from history pool (closed and canceled order).

Sample:
if(OrderSelect(12470, SELECT_BY_TICKET)==true)
{
Print("order #12470 open price is ", OrderOpenPrice());
Print("order #12470 close price is ", OrderClosePrice());
}
else
Print("OrderSelect returned the error of ",GetLastError());