How to transition your website from HTML/CSS to WordPress?

Having a brief look at your profile, it looks like you haven't taken any PHP. In order to create a WP theme you are going to need to learn some basic PHP. I would also recommend installing and setting up a local web server to run WP on rather than using a live hosting account. I personally use the xampp server (cross-platform Apache MySQL PHP Perl stack), but if you take the PHP courses they will show you how to install MAMP (Macintosh, Apache, MySQL, PHP). Either is fine, and if you're running Windows you can install MAMP for Windows, or just install WAMP. Once you have a local web server running, installing WP on that server is not difficult. Then turning a static HTML site into a WP theme is a matter of using the correct PHP functions to organize the templates for your site. But if all the stuff that I am saying sounds overwhelming or confusing to you, I recommend: 1) go take the Beginning PHP track; then, go take 2) Beginning WordPress track. After doing those you will have more than enough base knowledge to understand a tutorial on how to do what you want. Or alternatively you could then 3) take the Development for WordPress track where you will learn how to create WP themes and plugins from scratch. Happy learning!