Once you've started to become comfortable programming with core web technologies (like HTML, CSS, and JavaScript), and you start to get more experience, read more resources, and learn more tips and tricks, you'll start to come across all kind of tools, from JavaScript frameworks, to testing and automation tools, and more besides. As your web projects become larger and more complex, you'll want to start taking advantage of some of these tools, working out a reliable toolchain to give your development process superpowers....different types of code and how to fix/mitigate those, what tools are...useful in helping you test and fix problems, and how to use automation...