File system information source

Does anyone know a good source to find out all about the file systems with web development, such as linking files, appropriate file extensions and using different technologies together?

I’m not sure I fully understand what you are asking. However, file extensions are just indicating the type of file, which can be totally arbitrary as long as your code knows how to utilize it. In your operating system it associates different default programs with different file extensions so that when you double click on a file it opens it with an appropriate program. In windows 10 if you go to Settings then Default Apps and then “set defaults by app” (scroll down for it)…you will get a brief description of all the common file extensions as well as what the default app for that extension is on your computer. I hope this helps.