About Robotx txt

[tanzeelniazi]

Hello all
I want to know why robots.txt file is necessary ?
Is this for SEO ? or use in security ?
When i open my robots.txt file i see this
#Begin Attracta SEO Tools Sitemap. Do not remove
sitemap: http://cdn.attracta.com/sitemap/2*****0.xml.gz
#End Attracta SEO Tools Sitemap. Do not remove

i dont know what is this and dont know what before add :(
When i search vbulletin robots.txt i see this

User-agent: Slurp
Crawl-delay: 5


i want to add good things in my robots.txt file but i dont know what is the uses
Please tell me in simple words or make a robots file for me
thanks

--------------- Added 1442799540 at 1442799540 ---------------

Before i have good guests and bots like alexa bot google bot many other and before i have good alexa rank and traffic now bad
please some one make a good robots file for me pplease

[Max Taxable]

It's not "necessary" and also does nothing at all for security. It's just a signpost that says "please bots don't index any thing on this list" and few search engines pay any mind to it.

It's not a blocker, it's not a security measure, it's just a .txt file that "noble" search engine spiders do check and try to follow the guide of it.

[RichieBoy67]

It is always good to use it though many seedy search engines ignore it. The main searches though like Google and Bing honor it. Those are the ones you care about really. Others you can use htaccess to block if you are concerned with them.

You can use it to block pages you do not want indexed in the Google, etc. For example if you have a really spammy advertising section or something. You also add your sitemap there to keep google crawling it though you should have your sitemap submitted using webmaster tools anyways.

On my sites I use it to keep the focus on my topic content. SEO is about quality, not quantity so I do not index my off topic forums.

Also, as done in yours you can use robots.txt to put a delay on search bots if your resources are limited.

As for Attractaca.. I would not waste time using that.

[tanzeelniazi]

which sitemap is good for me ?? how to find more sitemap in my site ?
if i upload another sitemap any loss in my site ? or decreasing rank ?

[Seven Skins]

Sitemaps don't usually have any affect on site ranking ... If you want to add sitemap to your site with vbulletin then add something like this to robots.txt.

sitemap: http://sitemap_1.xml
sitemap: http://sitemap_2.xml