A file is some data that is stored persistently as a named collection on a storage medium - like a disk-drive:
A Qlik Sense App is stored in a single QVF-file. For more information look here:
Qlik Sense like most software make use of a range of different temporary files - more than you would care to think of. The handling of these along with also deleting old ones is usually handled automatically so you don't have to worry too much about it - unless of course you are out of disk space.
Files on disk doesn't consume memory the consume consume disk space or if you like "persistent memory" in contrast to volatile memory. The latter is in most circumstances referred to as just "memory" and the former to "disk".
It is rather seldom that there is a full and complete documentation on all the uses of all temporary files regarding a software package although the folders where they reside should be documented. The folder names reflect what they are used for when it comes to Qlik Sense.