Link & Meta Tags in HTML

The most important tag in the head of a web page is the title tag, but the link an meta tags can tell a lot of information about your content. These tag can tell important information to search engines, and provide a handful of usefulness to a visitor. HTML is not simply intended to hold content, it contains data to describe itself and reference more content. Text on the web is not just linear, its hypertext. It wants to quickly branch off like a textbook with chapters, pages, indexes and glossaries. The web is intended to be consumed in different ways by different people. The link and meta tags tell how a web page fits in the hierarchy of a website.

Read the full article here: Link & Meta Tags in HTML

I can figure out MOST of them, expt fr a couple...

Meta title, meta description meta keyword is very important for seo, search engines see meta title and the keyword in it.
Meta description show in ranking - so user can read it and go to your website