I’m sure you can use the googles to find one. But I don’t think you need to do that. Just follow the instructions very carefully.
“Nest a self-closing link element in the head element.”
A link element is just another type of HTML element, just like a body element or meta element. The link element is self-closing, like the meta element, so it doesn’t need a closing tag, just an opening one. You’ve added a meta element already so I am confident you can add a link element.
“Give it a rel attribute value stylesheet and an href attribute value of styles.css.”
These are just attribute/value pairs you add to the opening tag, just like you did with the charset attribute on the meta tag. Follow that same format to add these attributes on the link tag.