The Raspberry Pi is a small cheap single-board computer. It runs the Linux operating system which offers a powerful command line interface that mimics the one provided by the UNIX operating system. That was designed about fifty years ago and has remained very stable since.
There are all sorts of versions of the Raspberry Pi, aimed at different applications. The Raspberry Pi 4 model B and the Raspberry Pi 5 can be used as desktop computers. The cost for a complete system is around £100.
Many companies supply Raspberry Pis. In the UK this one is quite popular.
Raspberry Pis are usually sold as kits, which puts off some potential buyers. However, the assembly process is simple and quick. You can get a Pi up and running within about half an hour.
I assume that you have never done anything like this before, which is the safest assumption, and I give the instructions in stages, explaining stuff that you may not already understand. That can get a little long-winded. Don't be daunted, just go through the pages step by step.
The Pi offers a graphical user interface which is very similar to Microsoft Windows. It's also possible to run the Pi "headless" - without a keyboard, mouse and monitor. In that context it's controlled over the network using the command line interface.
If you're going to run you Pi headless then you need to be able to connect to it over the network and control it from another computer. To allow that you need to create a couple of files on that other computer. As we'll see, you need to do that first. I explain what to do here.
The Pi uses a micro-SD card for its permanent storage. These are often used in digital cameras to store pictures.
There are lots of videos on YouTube explaining how to assemble a Raspberry Pi and install Linux on it. This one is quite good, except that it assumes that you know all about using an SD card. I give bit more detail about that later.
Documents about the Pi often suffer from another assumption, which is that the people reading them already understand how to use one, in particular, how to use the command line interface and the commands that it runs.
This problem was recognised when the UNIX system was developed in the 1970s. The designers addressed it by producing a piece of software called learn which provides basic training on the commands and how to run them. Fifty years on the learn software looks a bit antiquated but it still works well because it gets the user to run commands and experiment on a real UNIX system.
The learn system fell out of use but a few years ago I got it working under Docker. Docker provides a UNIX system running within another system including Microsoft Windows, which means that you can run learn before buying your Raspberry Pi. Find out all about the learn software here.
Once you get your Raspberry Pi kit, the first step is to "burn" (write) the operating system onto the micro-SD card.
The micro-SD card
Burning the operating system image
Setting IP Addresses