FILES APP - what files get saved there and where do they come from

I have no idea how to use this files app. Is this a way that I can see all the (word doc) files on my PC? that would be very helpful. What files get stored there? (there are a couple but I don't remember 'putting them there' as I dont know how to use this app and never have). I've looked at tutorials but they're not helpful. They talk about how to USE the app but dont answer my question as to how the files got there in the first place.