Without information what you already know, your background, what you try to archive, which languages you to learn there can only be very generic answers. The same question on a web search engine gives many tutorials, list of tools and books.

I know a bit Python, Flask, HTML5, and CSS3. I want to learn web programming so I can get freelance work.

That's an excellent start, you already know a good set of languages. I found this guide useful https://github.com/kamranahmedse/developer-roadmap (discussed in https://news.ycombinator.com/item?id=18874028)