Also Read: Set current time as Android lock password
1) Create a new folder anywhere you want.
2) Right-click on the folder and select Properties -> Customize tab -> Change Icon and after select one of blank icons from icons list.
3) Now we need to hide name to make it 100% undetectable. Right click on that folder and select Rename. Press Ctrl on the keyboard and type 255 ( Ctrl+255 ).
4) And you can see now folder is completely hidden.
To find it, go to that directory where the folder is placed and hit Ctrl+A to select all icons from the directory.
You can add any files to a hidden folder and keep them safe.