To add a transaction, tap on the "New Transaction" button on the button bar. It is the first button on the left and looks like a sheet of paper with a star burst on the top left.
This brings up the transaction detail page.
To learn about all the fields on the transaction detail dialog click here.
Once you have filled in the appropriate information on the Transaction Detail page, click the OK button to accept the information and add the transaction. If you do not want to add the entry, simply close the window.