I I am a new user of iPad, can anyone assist in how I can print material ... Say a letter I have written ... When I try to print it says it cannot find a air printer, I do have a wifi canon printer but don't know how to link it. Any assistance would be welcomed

To use Air Print you must have an Air Print enabled printer.

There are apps in the app store which will let you print with other printers. There are a lot of them, download the free versions first to make sure the app works with your printer before you upgrade to the paid app, as not all work with every printer.

Some printers are directly compatible with AirPrint on the iPad. If you want this feature be absolutely certain the printer supports AirPrint before buying. Some printers may require a firmware update to work. These are usually available on the manufacturers site. If you get this* kind of printer you can print directly from within apps that support the feature, which is many.

iOS: AirPrint 101

Of course some of us already have printers and do not want to buy a new one. There are several ways to do this.

One is to use a printing app on the iPad.

Most (or all) other print apps can only print pictures and/or files that have been copied to that app via Open In or other method. Print n Share used to be able to print from AirPrint enabled apps if it was loaded the background. It lost this ability with iOS 5. It may still work with iOS 4 if you get it before the app is updated in the App Store. Several printer manufacturers have their own apps for their printers. In general those apps will probably have the best results, quality wise.

The second method is to load a program on the computer that will emulate an AirPrint compatible printer. Your computer must be on and have the printer available to it. The cheapest (free) is Airprint Activator. More features can be had with FingerPrint (mac and windows) and Printopia (mac only).

There is a third way. A few printers (mostly HP's again) can be set up with their own email address. PDF attachments can be sent via this address to be printed. The last review I saw (several months ago) said it could be quite slow (big files not recommended), and sometimes the emails got lost and never printed. The advantage was that you could literally send/print from anywhere you have an internet connection.
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There is a new wrinkle for small business owners and those with more than one printer who would like all their printers to work, but don't want to leave a computer on all the time. The Lantronix XPrintServer is a small box that connects to your network and is supposed to detect and make all your wireless printers available to iOS as AirPrint printers. I haven't seen a full review on it yet, so do your research.

A brand new option for lucky owners NetGear routers. Some models support NetGear Genie, which will add AirPrint support for all wireless printers on your network.