Stylesheets are CSS files that add color and style to your webpage. They can be linked by using the <link> tag, seen here
The way you link the stylesheet though, is only with one tag, no ending statement. The <link> tag has two parameters inside of it, rel and href. For a stylesheet, the rel needs to be set to "stylesheet" and the href as the path to your css file.
Example:
<link rel="stylesheet" href="my-style.css">
This would link to the file "my-style.css" and apply any rules set within. Now, its time to learn how to make those rules.