How can I create links between different areas of my knowledge?

I found an article online, this is a part of it:

Your knowledge about servers, networks, hosting environments, algorithms, data structures, programming languages, and databases should be absolutely clear before you move up your stack.

And most importantly, you should be able to create the link between each piece of the puzzle.

I know bits here and there about html, css, php, bootstrap, javascript, python, django and some MySql.

Now I want to start a project on my own. But I don't know how to take advantage of my knowledge and where to start. How should I plan for the website I am trying to build? How can I assess the visitors of my site?

Any help is appreciated.