To add to the confusion (or maybe not):
open the app File Manager (comes with the phone)
scroll down, look right for the button 'Clean junk', press it.
Here you can clean:
-stubborn junk
-number of caches (a summarized total, but also specified by type)
-add junk (again: a summarized total and specified by type)
Furthermore, top right has another button: 'advanced'. Most of the stuff here is obvious but i haven't really done anything here yet.
In this section, again there's a button on the top right, 'My Files'. It allows you to, well, find your files. Also, it shows 'app files' but again, i haven't really done anything here as of yet. So i don't quite know when files are being shown here or when to use this instead of the File Manager itself.
One final remark. Let's go all the way back to the File Manager where the button 'Clean junk' is. To the left of that button is a button 'PC File transfer'. I wish i had known about this when i was fiddling around with usb connections to put stuff like music on the S7 (I haven't found this trick online) because it's really handy. Example:
I have a pc that gets its internet through a ethernet cable. My phone connects with wifi to the same modem/router. I activate 'PC File Transfer', i open a browser on pc, and type the address and port that the app shows. I can now browse the phone from my pc browser (and transfer files). No need for third party apps (that sometimes have file size limitations)!
The only thing is: you must keep the app 'PC File Transfer' active on top. The service stops right away if you open another window on the phone (but it can immediately be started again, without having to open another browser window on the pc).