hi there jessica, well this depends on the platform your are using.
if you not want a particular page to be indexed in google then instead of modifying robots.txt try a noindex tag at header. a basic robots.txt should also be there at root all the time.



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Tier 5

Robots.txt file is a simple text file that must be placed in root directory of a website. The robots.txt file is useful in keeping your spiders from accessing parts folders and files in your hosting directory that are totally unrelated to your actual web site content.

Robots.txt are really important for make your page private. Robots file are very important to add for every domain. You must add this file to your website.

Hi

This file helps site owner in restricting the pages he/she does not want to crawl or index for neither as a page or update.It is done for search engines.

Thanks
ESTI

Robots.txt files are used to give an indication or command to Search Engine Robots that the site or a webpage is to follow or not to follow; index or not to index.

Robot.txt file is used in on page SEO to indicate Google spiders that which web page is to visit and which page not to visit. The pages which are restricted to be visited cannot be indexed by Google.

Dear all,
The Robot Exclusion Standard, otherwise called the Robots Exclusion Protocol or robots.txt convention, is a gathering to exhorting chipping in web crawlers and other web robots about gaining entrance to all or part of a site which is generally openly perceptible. Robots are regularly utilized via web indexes to arrange and document sites, or by webmasters to edit source code.

The Robots.txt File lets you control what search engine spiders should and shouldn’t crawl on your website. It’s a file that many WordPress users forget to add. For those who do, it can be unclear what folders should and shouldn’t be blocked.

Robot.txt file is helpful for you if you want to hide any contents from search engines. Like any personal data you have on your website, but you don't want to show them another world the use robot.txt. Mention your data on reboot.txt then searches engine will not crawl it.