The Title Tag and the Meta Tags are all placed in the head tag at the top of the page. The data placed in the Head Tag is not displayed in the browser. The Title Tag is the most important tag in terms of SEO, and the Meta Tags for Description and Keywords play more minor roles. They can play a part in the search engine results snippit. In a video Matt Cutts at Google explains the snippit.
The Robot tag which was introduced by Google informs the search engines whether or not to index or follow the page.
<title> The Title of the Page</title>
<meta name="description" content="description of page" />
<meta name="keywords" content="descriptive keywords" />
<meta name="robots" content="whether to index or follow">