With this button you can print your current Project on your local printer.
When pressing the Print button, a dialogue window will pop up and you will be able to choose your local printer and just start printing on a sheet. All the white canvas will be printed and not only the area inside the grey grid.
You may want to install a PDF creator that simulates a local printer. This way you have a stronger control over the final print: you can export the Project in PDF to save it for future prints without running the tool; share the Project without sharing the source file (for example for copyright issues); and see how the printed image looks in advance.
Before creating a PDF file, remember to change the settings in printer proprieties so that the file would be produced at 300dpi (a standard value of 600dpi would create a huge file). Moreover some PDF creators let you choose the final quality of the images: select always the best quality.
Remember! Set properties to save at 300dpi!