You may create more subdirectories as you see fit. It is usually a good idea to create directories to better organize your work. For example, if you are taking an English composition course you may wish to create a directory in which to place your compositions. Additionally, your server account is a good place to back up important files. Privileges, Protection and Access.
Computers are potentially vulnerable to unauthorized access by unscrupulous individuals.
Because of this computer operating system manufactuers build security systems into their operating systems. It is beyond the scope of this web page to delve very deeply into configuring your computer's security software. You cannot, in fact, modify the security settings for your server account. They are as explained above. Briefly, whatever files you want protected put into your Private subdirectory and whatever files you want public put into your Public directory.