Metadata are tags that add semantic information to your page such as a despcription of the page, the author. These tags go between the <head> and </head> tags and look like such:
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<meta name="keywords" content="a list of words pertinent to the subject matter of the document">
<meta name="description" content="description of the document">
<meta name="posted" content="date of the document is posted on the Website">
<meta name="author" content="content author of the document">
<meta name="updated" content="date the document was last updated">