CSS is a language that adds style (colors, images, borders, margins…) to your site. It’s really that simple. CSS is not used to put any content on your site, it’s purpose is simply to improve the user experience of the website. The most effective and common way to add styles to your website is by linking a the designated stylesheet to your page (as seen in the example below). This link is added between the head tags in the HTML file.
<link rel="stylesheet" href="whatever.css" type="text/css"/>
As of now we are on the third edition of CSS. This is a very good thing. Not too long ago, you had to take some very creative steps just to add rounded corners on a container or button. CSS can also be added directly in your HTML page by using the style tags listed below.
I only use this method on very rare occasions, and I do not recommend using it if you are just starting out. CSS is not at the forefront of programming languages, but there are entire websites and online communities dedicated to this language.