Please explain me Saving / Loading data logic (Serialization)

In my game, I have 24 collectibles prepared to collect. I need all of them to write to some file and read in proper time (for example when choosing level, where collectibles should be displayed like 1/3 collected in t$$anonymous$$s level or somet$$anonymous$$ng like that)

For the last 3 hours I am trying to understand serialization, JSON, XML, Binary, but I do not quite get it. I need to create a List (or array) to store the collected objects, they should have the ID of collectible (integer) and true / false statement (bool), whether collectible was already collected.

I prefer some solution, where I can "see" and browse in file, change values to true / false and test the game behaviour. Like XML or JSON.

I tried to follow some tutorials like t$$anonymous$$s one https://gamedevelopment.tutsplus.com/tutorials/how-to-save-and-load-your-players-progress-in-unity--cms-20934 but I could not understand the logic.

Can someone please explain me how to ac$$anonymous$$eve t$$anonymous$$s? Collectibles are spread to many levels.

Any advice would be appreciated.