If I import from my computer, do I need to assign header in one (like Buy/Sell), then in next screen do I need to clarify that B is open to long and S is sell to close?

You can see unmatched transactions warning during the import procedure. TradeMax identifies transaction into 2 pairs: a Long Trade, contains Buy to Open (Open Long) and Sell to Close (Close Long); a Short Trade, contains Sell to Open(Open Short) and Buy to Close(Close Short). Not every broker is reliable when it comes to the accuracy of their statements. Many Brokers mark Open Short and Close Short as Sell and Buy. That will confuse TradeMax during the trade matching, because Wash Sale rule only allows carrying loss between Trades with same intention. Therefore, one of your options is to manually alter these trades’ action type to get the correct results and to avoid the unmatched transaction warning. Insome special cases, you can change it to Short and Close Short (e.g. 100+200 short, then a 300 Close Short). The unmatched transaction warning will disappear by such adjusting.