In the trade screen you record trades that are made on an exchange for cash. (fiat currency) You can select either buy or sell here.
On this screen it is possible to unclassify existing transactions; this will preserve the main information of the transaction and will allow you to reclassify it as a different type of
transaction without needing to re-enter it. i.e. Trade -> Unclassified -> Make Purchase.
You can auto use the auto-value feature for looking up historic values. Note that for a Trade transaction where fiat (real) money changed hands you should book the actual amount.
For more information on auto-value click here.