Click on the skinny orange button if necessary to expand the left column;
Click on the tool icon for Page Details (a white "i" in a blue circle) in the orange block at the bottom-left.
You will see a variety of information about the current page, and will have the opportunity to change some of it. In particular, this dialog permits you:
to withdraw a page from public view entirely (to "deactivate" it):
if it complains that you or someone else are working on that page in another browser session, select "Work on this page (all changes)" from the View menu, and then try again to deactivate it;
after deactivating, the page will display with an orange "Activate" button at the top-right;
to examine the templates from which this page is derived; see also the discussion of walking the template hierarchy.