There are many articles and videos available explaining the skills that are required to become a web developer in 2018. In this article, I'm going to keep it very simple and tell you which technologies you will need to know and which technologies you can learn over time.
Make sure to have some fun after learning these fundamentals and create yourself a blog or a portfolio site. You will be practicing these fundamentals every day.
Hammering down the fundamentals will help you when you venture off to more advanced and new programming languages. These fundamentals will be your foundation. Every website you build will be based on this foundation, so make sure it's a super solid foundation ;)
After you have a sharp grasp on the fundamentals you will probably want to work with some tools and frameworks that make your life easier. You may want to checkout some popular frameworks such as Laravel or Vue JS. You will also want to checkout some build tools such as Webpack or Gulp JS. You may also want to learn some popular technologies such as Go Lang or Python.
There are so many other frameworks and libraries available, so check out the technologies that you find interesting and jump into the documentation. You will not have time to learn every technology under the sun, so find one that you enjoy and get really good at it.
Bottom line is to learn the basics:
Then you can move onto more advanced technologies.