Website Meta tags are text that describe what a page or article is about, and they are very important to SEO, search engine optimization, with out meta tags google bots and people searching the internet will have no idea what your website content is about, the meta tags describe the content before you open the page to read what the rest of the page contains, so great tags will entice visitors to click on your url instead of others.
There are meta tags located in various locations all around a webpage, site wide meta tags include the site meta description, this is the global description for your website and site meta keywords, which have no relevance any more to google anyway so you can leave the keywords tag blank, the robots tag should be set to index,follow to allow google to index your website, these settings are located in global configuration in the back end administration.
Menu items include important meta tags for your site, the browser page tittle is what is seen in your browser at the very top, and is used by search engines to find your website, the browser page tittle should include your keywords, the meta description should describe your pages contents and once again include your keyword or keyword phrase, the meta description is visable in the search results page under the browser page tittle so they are very important for seo.
Articles contain important meta tags particually for blogs, they are essential for seo and for search engines to index your pages, the article tittle and alias play an important role, and under publishing you will find the meta description tag, the meta description should contain your article tittle along with your keywords and it is important to use keywords only once though out the website, so it pays to write down your keywords and tick them of as they are used to prevent duplicates.
The meta robots tag are also important they as they tell the search engines if a page or article in your website should be indexed or not, index,follow means to follow the links and index them, this tag is the most widely used, no index follow do not index the link but follow the link to the next one, the no index follow would typically be used on duplicated content in your website, so the content will only be indexed once but the link will be followed to the next one, index,no follow means do index this link but do not follow the link to the next one, this tag is seldom used, no index,no follow do not index the link and do not follow the link again seldom used in a website.