If you have a airprint printer or something like that you can print right from your iphone if not you need to connect your iphone to the computer and open the picture with some program on your computer and print it from there.
Some wifi printers have apps that allow it but only a few right now. Kodak does. I usually either email it to myself or copy it from my phone to my computer and I find it does a better job. Maybe they will get better with this.