To print/email/fax transactions immediately when you record them, click the Sales and Purchases tabs in the Preferences window, then mark the box labeled "Automatically Print Sales/Purchases When They're Recorded." Choose which method you wish to use automatically -- Print, Fax or Email.
If you choose to print sales and if you want to print packing slips and delivery or mailing labels to accompany your sales, consider marking the boxes labeled "Print Packing Slips (or Labels) When Invoices are Printed."