There is a C language module called FATFS, but do you know its algorithm?

I'm trying to create an operating system as a hobby.
I am currently trying to build a file system on that OS.
The languages are GCC and nask.
I'm thinking of referring to FATFS, but I have little knowledge of C language and
Of course, I am studying C language, but it is difficult to learn, and the program that I can make is
It only displays a string on the console.I understand the pointer and structure just in case.
That's why I want to hear the FATFS algorithm.
I'm sorry that the writing is dirty.
P.S. The core of the OS exists by referring to the book "Introduction to OS Self-made" which can be made in 30 days.
　　　I understand the source code.