Page setup is a very important utility of MS-Word used to set up the margin, the paper size and the layout for active file. Page setup option provides you three options. You can see the page setup window in figure
Margins, Paper and Layout Margin:- In margin you can adjust the top, left, bottom, right and also if you want to provide some space for the binding you can adjust the gutter position.
Paper:- In the paper option you can adjust the paper size what is required(A3,A4 etc), you can also adjust the orientation of the page if you want it portrait or landscape.
Layouts: in layout you can adjust the layout like where you want to place the header and footer in your page or in which page you need the header and footer. You can adjust the vertical alignment of the text between the header and the footer. You can see all your changes in the preview.