It has 2 options. keywordscontent And description. When a spider/Google bot finds your website, it scans the meta tags, mainly for these functions. keywordscontent has a list of keywords, separated by commas (like blog,sir_Furious,geek's,geeks,haven EtC.)
The description property tells people a summary of your website. Like this.
<meta name="description" content="Blogger is a free blog publishing tool from Google for easily sharing your thoughts with the world. Blogger makes it simple to post text, photos and video onto your personal or team blog.">
The content tag is what the actual thing is. The name tells the bot what it's reading, and what is in the quotes is the actual content. (No WAY! NEver of guessed from the content taghs huh?;P)