Let’s say you want to hide a folder in your Documents folder called “MyStuff.” You can do it simply by launching the Terminal (found in your Utilities folder inside Applications) and typing the following:
chflags hidden ~/Documents/MyStuff
Once your MyStuff folder is hidden, it will not appear in the Finder, but it will still be accessible via the Finder’s Go>Go to Folder (Command + Shift + G) and typing in the path to the folder.
To unhide your MyStuff folder, simply type the following:
chflags nohidden ~/Documents/MyStuff
If using the Terminal isn’t your thing, you can download Hideaway, which does the same thing, only you just click a few buttons instead of typing code into the Terminal.