Among other things, the iPad is a great way to save paper: It lets you carry around all kinds of digital documents that you might otherwise have had to print.
But from time to time you may still need to print data that's on your iPad--business documents that you created in Pages and Numbers, for example, or driving directions to hand someone who's not packing silicon. Printing from the iPad can be easy if your needs are modest, but even if you require extensive printing control, there is, as they say, an app for that.
(The following steps work for any iPad, including the iPad 2 and both Wi-Fi and 3G models.)
Even though you can add a USB port to your iPad with Apple's iPad Camera Connection Kit, it's no use plugging in a USB printer, because iOS doesn't know how to talk to printers via USB. Some printers have built-in Wi-Fi (a natural match for the iPad). But for the rest, you'll need a computer or other proxy device to serve as a conduit for iPad print jobs: your iPad connects wirelessly to your Mac (or other device), and that in turn connects to the printer.
But the communication channel is only part of the picture; you also need software that knows how to send data to the printer in the right format. Starting with iOS 4.2, Apple built printing support into the iPad with a technology called AirPrint. Any app that has been updated to take advantage of AirPrint can print wirelessly to a compatible printer with a couple of taps.
For reasons that only Apple knows, the initial implementation of AirPrint works with just a handful of newer HP printers that support something HP calls ePrint. If you happen to have such a printer (HP has a list of them on its Website), and it's on the same local network as the iPad, your iPad will be able to see it and print without any special configuration. (ePrint also gives your printer a private e-mail address, so you can also e-mail a document as an attachment, and it'll print automatically.)
If you aren't fortunate enough to have an HP ePrint-compatible printer, however, you can still use AirPrint with the vast majority of printers. All you need is a bit of extra software that runs on your Mac.
Two such applications are quite similar: Collobos Software's FingerPrint (US$8) and Ecamm Network's Printopia (US$10). Install either of these utilities on a Mac on your network, select the printer(s) you want your iOS devices to be able to use, and you can then print to those printers from your iPad just as if they were HP ePrint printers. Both of these tools let you print from your iPad to any local or network printer; they also let you use the Print command to send documents to your Dropbox or a folder on your Mac in lieu of a printer.