Hi mom….
I have no idea where you heard about CSS but I am assuming it was somewhere in Facebook. So let’s take Facebook for example. If you go to your profile, you have a cover photo, your profile picture showing in a small thumbnail, then below you have your timeline and your intro and other contents. So, before the page looked like this, it was probably written in a much simpler language that laid out the contents of the page, that probably distinguished the headers, subheaders, profile picture, cover photo and other elements. What you see now - the different background colors, font sytles, images and their placement, is all CSS. So, in that sense CSS is like a skin that adds an appearance to the page so it is visually pleasing to the users. You may also think like the page being a skeleton and CSS the skin. Most probaly, the primary language used to write the page would be capable of styling it too but CSS makes styling easier and less time consuming as similar elements can be grouped and styled together. Similarly, a style can be created and applied to various elements across the page. I have heard that CSS has become more versatile and powerful now and does more than just styling which I have yet to learn and discover.