First on the main screen, go to View, Gantt Chart, and Scale to Fit Project.

Next go to File , Print. Make sure to click on the arrow to the right of your selected printer so that all of the expanded options are showing.

Under content, you can select whether to print the Gantt alone or the Gantt and outline. Under Dimensions, make it 1 page wide and 1 page high and you are done.

If you want to change page orientation, you have to go to File, Page set up to change to landscape view.