You can show hidden files in Finder, then rename a file or folder with a period at the beginning of the name, then hide hidden files again.
To show hidden files in Finder, copy and paste the following command into a Terminal window, then press enter:
defaults write com.apple.finder AppleShowAllFiles TRUE && killall Finder
To hide hidden files in Finder, copy and paste the following command into a Terminal window, then press enter:
defaults write com.apple.finder AppleShowAllFiles FALSE && killall Finder