If you glanced at the table of contents and are feeling a little intimidated at how many topics there are, let me reassure you there’s no need to be. It’s almost impossible for any person to know everything there is to know within this field of work - so don’t believe that to be a good developer or designer you should master every topic here. I’m pretty sure that’s not possible.
What I’ve found is that the best developers - the ones who produce the best quality of work and integrate best with teams - tend to have something called a ’T’ skill set. Imagine we wanted to draw a bar graph representing your knowledge. From left to right are the various skills you have as a web developer, from top to bottom is the depth of your knowledge in those skills. Having a T skill set means the graph would look like a capital T: you know a reasonable number of skills to a shallow (but useful) depth, and have one or two closely linked skills where you have very deep knowledge. If you’ve chosen your skills well the deepest parts will be in the middle of your repertoire, well supported and surrounded by shallower skills which are relevant to the ones you know in great depth.
So, don’t let the breadth of topics within the web-development world scare you: You don’t need to do everything amazingly well. Be competent in as much as you can, and an expert only in carefully considered areas.
Those shallow skill sets are valuable, and knowing enough about the skills you’re not an expert in to communicate clearly with people who are will mean you’ll be able to find answers to problems quickly. People working on the web tend to be a helpful bunch and if you can ask clear and meaningful questions you stand to get a lot of useful assistance if and when you need it.
If you’re new to web development, try a bunch of things and see which you like most. Develop your depth there, and try to broaden your T from time to time.
If you’re managing or working in a team, the best often consist of people with T skill sets, where each person has a different but complimentary deep skill - I’d use some sort of analogy about Tetris and fitting together but that’d be a little contrived, so I’ll leave that to your imagination.
Whatever your current skill set, and wherever you’re wanting to go in this field; I hope you enjoy getting there, and I hope this section of my site helps point you in the right direction. Constructive feedback is always welcome via @mattwilcox, though please note I won’t be able to answer specific coding problems for you, sorry.
Good luck, and have fun!