The 'grey area' to the left of the working area (which is blue on my machine) shows the thumbnail of the page where you are currently entering or editing text. The only way i know to make it go away is to go View (menu) > Hide Page Thumbnails.
The grey vertical stripe to the right of the working page in the area beyond the edge of the defined page width set in Page Setup. It will show whenever your document window has been set wider than the page width at the current magnification.
You can remove that grey by enlarging the page, or by reducing the window width.
Pages documents align to the left edge of the working space in the window, and can't be moved from there.
Other actions you could take:
Use Full Screen mode (View > enter Full Screen) The removes all other material from the display, leaving an image of the page, centered left to right, and surrounded by a blank, black border. Depending on your window settings, you may also see a word count and an page number/page count displayed at the bottom of the screen.
If you want a plain, whiite (or other colour) margin for your document, try this:
Open a new, blank Pages document.
Use the View menu to hide all elements whose menu item starts with "Hide".
Set the view scale to 400%, using the control at the bottom left.
Drag the window to the left about twice as far as needed to hide the red amber and green gumdrops in the title bar.
Drag the control at the bottom right corner right (and down) to fill the window.
Drag the title bar right to hide the lozenge at the right end of the title bar.
Save the document as a Template, with the name "Blank white background"
To use:
Open ths template, then open the document you want to work on. Hide the Page Thumbnails of the work document, resize the document window to hold the page, with no grey area to the right. Reposition the document to be centered horizontally on the page.
Regards,
Barry