The internet is like an ocean. Vast. Full of life, things to interact with, look at, take.
The computer is like your own personal submarine. It can do lots of things, and one of the main things it's used for it to explore the ocean.
The browser is the periscope. You use the browser to see into the ocean.
The mouse is like an robotic arm attached to the sub, that moves around and interacts with things in the internet. What you tell it to do, it does. Point, click, drag, etc.
The address bar is where you type in the coordinates that tell the sub where to move to next. The enter key is the launch button for the thrusters.
I think this is a good metaphor because it uses the theme of exploring a vast, new world. I assume prisoners, especially men, would enjoy the idea of operating a piece of machinery like a submarine.
Hardware is anything on the sub that you can touch.
Software is anything on the sub that you can't touch.
(For those concepts, I would use a CD player as the analogy. The CD player is the hardware and the music is the software. Yes, the music is on the CD but you can't touch the music. You can only "hear the music" or "run the program" by operating the software in the hardware.)
Now, there are lots of other things that you can do on the sub. You don't have to spend your whole day looking into the periscope.
The sub has a gigantic work bench area, with many different types of tools. It's a place you can go to make things. Each thing that you or someone else makes to be used on the submarine is called a file.
Files are made of different materials. Some are wood. Some are steel. Some are brick. These are file formats.
Depending on which type of file you are working with, you will choose a different tool. The tools are the programs. If you are working with wood, then you use a saw. If you are working with steel, then you use a welder. If you are working with brick, etc. These tools are programs like word, excel, etc. They allow you to shape and modify different files.