Most designers and developers use what is know as a ' Frame Work ' as a starting base for the site.
Bootstrap is the most used framework http://getbootstrap.com/
As with any sort of programming you should never reinvent the wheel, within Bootstrap you have easy to use pre written code which allow you to simply create the frontend for common website elements such as layout control, forms, drop down navigation and and modals. If you have a basic knowledge of HTML and CSS you should have no problem using a framework.
If you interested in back end development (databases powered content, login systems) etc are more complex to learn and you will need a solid understanding of PHP.
Wordpress does provide many codex code's which will make backend development easier.
The main thing you need to understand about creating web sites is the two different types of roles when designing a site.
Web Designers: These people are designers often they have little technical knowledge but are good at presentation, design, layout and UI design.
Web Developers: These people are technical and write all the code needed for the designers front end design and back end functionality.
My advice would be just start to design a basic page and improve it over time as you learn more.
Hope this helps