Where should I start preparing for a bright coding career?

I am in the last year of high-school and I want to start learning some very used coding languages. I am going to learn informatics at university but I want to do some things before I will get there. Where should I start? A friend of mine told me about Udemy but there are hundreds of courses on different topics and programming languages. My goal is to prepare for a well-paid job. What is your opinion about this?

Most people on this forum are studying using freeCodeCamp.

Also, check this article: https://www.freecodecamp.org/news/2019-web-developer-roadmap/