Disable page = Nobody can see the page. The page is removed from the menu and it can't be accessed with the URL. You see it because you're logged into the backend. That is also why you see the red sticker 'Preview', because it is a preview.
Hide in menu = Page is hidden from the menu and the sitemap, however, it can be accessed with the URL.
Check the following documentation: http://docs.typo3.org/typo3cms/GettingStartedTutorial/