Files and Folders and Extensions

What is on a secondary storage device (like on a hard disk)?
How is what is on the device organized?
What is a file, what is a folder?
How does the computer (or you) find a particular file?
What is the path of a file?
How would you find a file if you forgot where you put it (the path) but remember the name?
Files are pictured by different icons. What does it mean?
Sometimes (?) file names have a dot in it? What's the reason for this?
What is an extension and why is it necessary?
Can I change the settings to always see the extensions?
I have a new browser but if I click on a saved web page, still internet explorer opens the page. How could I change this?
What is a relative path and where would I use it?
What extensions (kind of files) do you know?