It’s really weird that one would like to do this but perhaps you are running some private website dedicated to just an intimate group. Anyway, you can stop search engines indexing your web pages by putting a meta tag in the header section of them:
<meta name="robots" content="noindex" />
That’s it. Any search engines abiding by the rules especially Google will never index this page or exclude all the pages with this meta tag out of their index database. You can also prevent search engines from requesting and reading your website or pages in the first place by the help of a robots.txt which specifies to what areas of your site are they not welcome.
Adding a rel="nofollow" tag helps too in that search engines will not follow this link to the destination page, let alone indexing it:
<a href="http://www.example.com" rel="nofollow">example site</a>