text-decoration is a CSS property that allows you to change the decoration of the text (“Oh, really?”) and when you set it to none like this: text-decoration: none;, it tells the browser to display the text with no decoration (“Captain Obvious”), so when you give your link (a) the property text-decoration with a value of none it will remove the underline that is there by default.
I think the colour part is a bit obvious, but if you’re wondering what #cc0000is, then here is your answer:
#cc0000 is what’s known as a ‘Hexadecimal colour code’, it’s just a code that tells the web browser what colour something is. I don’t know much but here is a link to the Wikipedia page on it.