Your message doesn't make a lot of sense.
I noticed that all users files are saved on that Home folder.
In the UNIX model, a home directory is the root of where a user's files are stored. It is an error to say "all users files" are stored there; you can have subdirectories, for example.
How can I create that so for every user creation to have sub folder for that user under home folder?
What are you trying to accomplish? For example, it could be that the answer is instead of specifying /mnt/yourpool/users/youruser for a home directory, specify /mnt/yourpool/users/youruser/subfolder
This really depends on why you want to do this and what you think it will accomplish for you.