Tutorial on Zoom functionhttp://www.beato.com/mac-word-2011-window-zoom-shortcut/

If the zoom slider has disappeared, you are probably not in the Print Layout view

To change your views, you must click on the View menu or the view buttons at the bottom.
https://support.office.com/en-IE/article/Views-in-Word-c39e6727-7a05-45f4-b4ec-48ac50fff220