The first thing you need to know about indexing your site at search engines is that you control which pages are indexed and which are excluded.
You do that with a file called robots.txt.
Robots.txt contains nothing more than a record of which robots should index which pages.
Without going into too much detail, there are two conventions used in a robots.txt file:
User-agent: [Defines which robots the site is addressing.]
Disallow: [Allows you to list the sites or robots you want to exclude.]
In general you are going to use “user agent:*” to make ure that you are addressing robots of every search engine and you’ll probably want include all of your pages (although you might want to exclude your directories “Disallow: /cgi-bin/” )

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yes its very important for seo