The iPad prints using WiFi. It was designed to print to an AirPrint compatible printer that is accessible on the WiFi network. See <iOS: AirPrint 101>.
A printing App would be required to print from the iPad to a non-AirPrint printer. Look for a printing App from your printer manufacturer at the iTunes App store. If one is available, it will probably have limitations but should get you printing.
There are pay Apps with more features such as Print n Share and PrintCentral. However, they can only print from within other Apps that have the "Open In" option. I have both. I think PrintCentral may have slightly more features, but the both work about the same.
To my knowlege, there is no way to print from the iPad over a direct USB connection. If it could be done, it would probably require an App that violates Apple's iPad programming rules.