Hide and Show Hidden files in MAC OS

Open your terminal (Finder > Go > Utilities > Terminal.app)

To Show all the files, including hidden files type in:
defaults write com.apple.finder AppleShowAllFiles -bool true
and restart your Finder, (Apple > Force quit ... > Finder [relaunch])

and to hide then again:
defaults write com.apple.finder AppleShowAllFiles -bool false
relaunch finder and you're done.