how to printing from iphone

you will need an airprint compatible printer - heres Apples official list:

http://support.apple.com/kb/ht4356

but if you would like a short cut you could try an app like print n share which should work for most printers:

http://mobile.eurosmartz.com/products/printnshare.html

Check the tutorial from pcmag

http://www.pcmag.com/article2/0,2817,2412773,00.asp

and troubleshooting steps here

http://www.apple.com/support/iphone/assistant/airprint/