The sitemap provides a structure for your entire website. The robots.txt then informs search engines which pages they should crawl. It is a root file on your site that helps search engines avoid blocked pages to display.
That said, the robots.tx does not secure information. For this, you might need to make a page private or even password-protect the page to ensure Google does not crawl them.
Also, when you use Robots.Txt, you often direct users to pages that are no longer there. If that is true, you need to create a custom 404 Error Page re-directing users to another website page.