I see VeraCrypt has an option to create an encrypted container with no filesystem. How is this possible? If there is not filesystem there, then how can I place my files or folders in the container? Is this an option for those wanting to place a single file in the container? Thanks.
How it is possible
You simply get presented a virtual volume (or virtual drive with a loop/raw/non-existing partition table depending on how you look at it) that has nothing on it. Indeed you can't directly put any folder on it but you might want to format it in another file system not offered from inside Veracrypt (e.g. exFAT, ext2 on Windows, UDF?). In fact you can think of the formatting as an extra service that has nothing to do with the encryption itself. AFAIK, Verycrypt itself does not care at all about the file system when you decrypt the container then. It simply just presents the volumne to the OS which then deals with it.
Like mentioned before you might want to format it some other way, maybe in some other format or with special settings. Or you have some complicated setup where you actually don't need any direct file system because you want to dedicate that volume to a database server or to be used as a raw disk for some virtual machine (which in turn lets you put a partition table and several partitions on it). Heh, now that think of it even some sort of software RAID solution should be possible.