CSS is used to style the content on a webpage. It can be used to change the colour, size, font and layout of elements on a page, and much more.
Notice how the <style> element goes inside the <head> element, below the <title> element. This is where you will put your CSS code.
Let's break it down: You can see that we are targeting HTML elements in our CSS (body, h2, etc.) then in curly braces we have what we want to change (background, font-family, etc.) and then a colon and the value we want to change it to (orange, verdana, etc.).
Please forgive the American spelling of colour! this is something the world just has to live with.
As with most things, the best way to learn to code is to try for yourself!
Start Coding!