How To Install and Configure Robots Meta Plugin
Tag is a Special tag which tell robots not to index any web page, and/or not to follow it.It is a method to tell search engine which is to be indexed,followed or no-index,no-follow any web page of your site.
Other meta tags are noarchive,nocache,nosnippet,noodp,noydir ,which have different function to do.Using meta tags in all pages is a lengthy and difficult task.However if you use WordPress as Cms then there is plugin called Robots Meta developed by Yoast which do the work for you.