Its to tell search engine spider about your website nature/subject moreover you can use it in directing spiders about what to read and what not. when to visit etc
meta tags represent information about information such title of the page, description, keywords. they can also be used to redirect the page but it is not recommended. there are hundreds of meta tags but everyone is not that important
They are tags which are not being shown for the visitors but they are shown for the SE. I believe that is the way to improve the keyword dencity and keep your web site content user friendly
Now a days, only meta description and meta keywords are relevent for SEO purpose: meta description tag is used to tell search engine spider about the webpage in brief and through meta keywords, you can make your webpage relevant for specific search queries.
Meta tag provides the information about the web page. It contains information about what the web page is about. It also helps the search engine to understand the content of the site.
hopefully by now, you know what's meta tags all about. if you are using blogger blog this is how u can add meta tags in your blog Adding meta tags to blogger(blogspot) blogs