With the free version of PrinterShare app, you can only print a test page directly to your printer. This will allow you to see if PrinterShare is able to communicate with your printer. If you would like to print directly to your standalone printer, you will need to purchase a Premium Key or PrinterShare Premium app.
You can, however, print your emails, documents or any other items using Google Cloud Print (you can choose it as your printer in PrinterShare by pressing menu button and tapping Google Cloud Print) without any restrictions (no Premium Key required).
You can also download the free desktop version of PrinterShare console to your computer and print 20 pages for free over the Internet.