If you look at the code for this page you will see that I reference a separate Style sheet file.
It is created in basic text editor just like the HTML pages we were learning to do.
When you save a stylesheet file you should give it a name (I chose 'styles') and then follow with ".css"
It is good practice to save it in its own subfolder - I named mine 'CSS'.
To call that file the href is css/styles.css