Hide folders by making them system folders on Windows
One of the basic things one does while configuring a Windows system is to enable viewing hidden files. So basically it is impossible to hide files by making them "hidden".
What helps against most nosy people though is to make a file a system file or folder - that way the tagged file will remain hidden even if "hidden" files are made visible (of course one can still make system files visible but few people will enable that since it's usually not necessary).
To tag a file a system file, open a command prompt by entering cmd into your search bar. Enter following into the command line, replacing the path I use with the one to your file (+s is for systemfile and +h is for hidden):
attrib +s +h C:\Users\howtoforge\Desktop\bla
To make it visible again, just turn the plusses into minusses:
attrib -s -h C:\Users\howtoforge\Desktop\bla