Given my affinity for using my Mac and my web servers via their command lines, I love this reference: Linux File System Hierarchy v2.0. Check it out and get a handle on those /bin, /etc, /usr, and /var directories.
What is a file in Linux? What is file system in Linux? Where are all the configuration files? Where do I keep my downloaded applications? Is there really a filesystem standard structure in Linux? Well, the above image explains Linux file system hierarchy in a very simple and non-complex way. It’s very useful when you’re looking for a configuration file or a binary file. I’ve added some explanation and examples below, but that’s TL;DR.