Tap on Cloud Print and turn the service on with the slider. If you've previously used Cloud Print, you'll see a list of available printers populate.
Open the Photos app, and locate the picture you'd like to print.
Tap the Menu button. This is located in the top-left corner on the Nexus 5, across the bottom of the screen in Google Play edition devices, and in various locations on other devices.
Select your Printer from the drop down menu on the printing pop-up screen.
Tap Print at the bottom of the pop-up screen to send the picture to your connected printer.