Linux itself, is a kernel, which is the heart of an operating system, and is what makes sure all actions are carried out smoothly. It also includes compatibility layers that allow users to run non-compatible programs on their computer, like windows only programs. Distributions of Linux include the actual desktop of a computer. They include everything your computer needs to function properly.
None of this means that Linux is actually like Windows or MacOS, in fact, it is about as different from them as it can be. Linux is based on a UNIX-based kernel, and functions completely differently than other operating systems, and has very different ways of handling files and processes. Linux is also open source, meaning people can view the contents of Linux and add onto it freely, while other operating systems make sure people can’t do any of that.
But, Linux isn’t just found on home computers. Linux is found on 100% of global supercomputers, and that’s not all. Android, found on many phones, is based off of Linux, meaning that most modern phones also run Linux as a kernel.
Linux also allows the connectivity of many very old computers to the internet, and is often seen as safer than Windows or MacOS, due to the thousands of people working on it. Every single person contributes many lines of code to the kernel, making it safer each and every day. This makes Linux a hard target for hackers and viruses, with most Linux based systems being invulnerable to the common types of viruses that are found on the internet or hidden deep within files.
On top of this, Linux allows the user to freely distribute it at their will, as it is in many cases free. There are also many different types of Linux, called distributions, and you can find thousands of them today, many based on one another.