With any technology, there is no reason to start with the version that was popular five years ago. Start learning with what is current. As of this writing, HTML5 and CSS3 are the standards. Begin here and work your way forward.
Create a simple WordPress site. Once installed and the website is up and running, change it piece by piece. Figure out what goes into the header tag. Learn how the navigation structure works, etc. There is no better tutor than real practice. If you have an actual site to play with, it makes it all the more exciting. You will eventually learn your craft and gain proficiency.
Start with the header tag and then the body tag. Then begin to fill in the gaps. Start at the top working on logo placement and navigational structure. The latter will keep you busy for a while!
Find excellent tutorials
There are plenty of good tutorials. Start with the free tutorials but move on quickly to substantial “pay” resources whether that is a book or a website.But be careful! Double check and make sure you are working with HTML5 and CSS3 material.
Use the Internet every day
Chances are you would no be interested in learning HTML and CSS if you were not already an avid web user. Continue to use the web every day. Visit all kinds of sites. View their page source and learn how they structure their site.