There are several ways, but why do you want this?
The Finder will be cluttered with these files and folders. If you need it on a temporary basis, use the Go to Folder... menu item from Finder/GO Menu and enter the invisible folder name...such as /etc, /var or /tmp or the home directory of all three.../private.
To display it permanently (or untill you change it back) you can use a utility such as Cocktail or type this in the Terminal:
defaults write com.apple.finder "AppleShowAllFiles" 'TRUE'
Type the above exactly as it appears, then press ENTER or RETURN exit the terminal and ForceQuit (ReLaunch) the Finder from AppleMenu-->ForceQuit Menu.
All invisible files, directories will be shown.
To change it back type the same, except replace TRUE with NO. Remember all quotes must be included and typed as shown, double and single quotes. Also, the command is case sensitive, so pay attention to case placement.
BTW, you're doing this as the user and not the "all powerful" root, so don't worry about damaging your system. This is a USER preference.
Have Fun!