One of two things will easily prevent most search engines’ robots from indexing your site:

1. add <meta name="robots" content="noindex, nofollow"> to the head of the document (“noindex” stops the page from being added to a search engine, “nofollow” tells the robot from following the links; either can be removed).
2. add a robots.txt file

The latter is a text file that indexing robots read to learn what parts off your site are “off limits.” Find out more about how to use this file, read A Standard for Robot Exclusion