Where to start Web Dev ?
If you are a complete beginner to web development, we'd recommend that you start by working through our Getting started with the web module, which provides a practical introduction to web development.
If you have a bit of knowledge already, the next step is to learn HTML and CSS in detail: start with our Introduction to HTML module and move on to our CSS first steps module.
If you are comfortable with HTML and CSS already, or you are mainly interested in coding, you'll want to move on to JavaScript or server-side development. Begin with our JavaScript first steps and Server-side first steps modules.
After mastering the essentials of vanilla HTML, CSS, and JavaScript, you should learn about client-side web development tools, and then consider digging into client-side JavaScript frameworks, and server-side website programming
For documentation of Web dev take help of mdn web docs:
https://developer.mozilla.org/en-US/docs/Learn
Git & Github:
All developers will use some kind of version control system (VCS), a tool to allow them to collaborate with other developers on a project without the danger of them overwriting each other's work, and roll back to previous versions of the code base if a problem is discovered later on. The most popular VCS (at least among web developers) is Git, along with GitHub, a site that provides hosting for your repositories and several tools for working with them. This module aims to teach you what you need to know about both of them.
For more information take help of mdn web docs.
https://developer.mozilla.org/en-US/docs/Learn/Tools_and_testing/GitHub