Linux is the kernel; that is, the core of the operating system, which handles memory, hardware, inputs... Every OS has one. Windows' is called NT, macOS' is called Darwin.

You don't use the kernel, you use the OS. Linux is special because there several operating systems based on Linux; they are called distributions, and they are what you want to use.

You can create your own Linux distribution, by bundling various software packages with the kernel, in a way that caters to specific needs or follows a philosophy (for example, Linux Mint is a distribution focused on ease of use, Archlinux on minimalism..). This is not possible with Windows because their kernel is not licensed under terms which would allow this. It is with Darwin, but unusual.

You can also create your own kernel but this is extremely hard. Getting the computer to boot is easy enough (relatively speaking), but getting programs to run and things to display is much harder. Getting your custom kernel to a usable state is orders of magnitude harder, as it needs to work on and communicate with modern hardware and networks. Linux took more than 30 years of development by thousands of developers (some of them highly talented in a very narrow field of computing) to get to the level it's at.