How do I add this snippets to my site?

Hi, how do I add this snippets to my site?
Where do I place the CSS info? Can I use a HTML Widget?

Well that depends on which CMS system or website builder you are using. You need to add all the code i.e HTML, Css and JS script code in  your webpage. 

Do you have a WordPress site? If yes, you can add "WP Coder" plugin which will help you add HTML, css and JS code. 

Alternatively you can also add custom template in your wordpress site. You may like to take a look at the following guide which should help you: https://wordpress.stackexchange.com/questions/203027/how-to-add-page-using-html-css-and-js