Yes, it has been a lot of information, but we have only just started. Overwhelmed yet? Good.
Your computer stores data on its disks in structures called files. Nothing new so far. You know the different file types, like documents, images, audio, video, etc. You need not worry about how the computer recognises them, and how it knows where on the disk it looks for your files, it’s all very simple. For you. But your computer does need to worry about it, or rather than worrying, just “know” what is what and where and how. The way these things are defined and accessed is determined by the file system in use. You could think of it as a specific way your computer stores data on a disk.