Google Cloud Print makes printing more intuitive, accessible and useful, by letting you print to your printers from Google Cloud Print-enabled apps on any computer or smart phone.
Google Cloud Print is available:
On any web page, if you see a “Print” button with the Google Cloud Print logo, you can print without leaving your browser.
On any mobile device: if you access Gmail or Google Docs through your phone’s browser ( go to m.google.com ), you can print any email, document, spreadsheet, or other Docs file through Google Cloud Print. Using the new print2docs feature, you can also "print" any file you wish to your Docs account for safe keeping. More Info »
From Google Chrome: you can print any of the open tabs on Chrome to Google Cloud Print by hitting Ctrl + P or "Print" from the wrench menu and selecting "Print with Google Cloud Print" from the destination dropdown. On the Chromebook, Cloud Print is the default print option.
Moreover you can see what application allow you to print to Google Cloud Print at http://www.google.com/cloudprint/learn/apps.html