I am just expanding Peter Scheler's better answer. Web Development is a vast topic. Start with the basics. Then you will need to decide your area of expertise. There are three main areas,
Frontend: You can't live without learning frontend. Sound understanding of how frontend is works is necessary. So learn it. Other than this, you will need to understand how HTTP works. If you want to work as frontend developer, you will need to get familiar with some frameworks like React or Angular and NodeJS with few other libraries. You can always learn them while working on some project. Learning to learn is the most important skill you should learn.
Backend: As I said before, you must learn some frontend even if you want to work as backend developer. HTML, CSS, JavaScript, and AJAX are important. For backend, you will need to learn a server side technology like PHP or Ruby on Rails. Also, a database management system that comes with in your chosen stack is a must.
Full Stack: Frontend and backend both are important aspects of web development. Some developers prefer to call themselves full stack developer but I think that no one can expertise in both. We all have good grasp over one field than the other. As frontend is now developed seriously, you should not bother learning both sides equally. Get a good understanding of both but focus on one field.
Frameworks: Frameworks pretty much depend on your needs. You should focus on learning architectural and design patterns instead of learning syntactic jargon of some framework. Then you can pickup any framework as required. Mostly team experience decides the framework for the project. So specializing in some framework will allow you to get a more targeted, less stressed job.