Here is the quick version:
1. Open up Terminal (you can find it via Spotlight or in /Applications/Utilities/Terminal.app)
2. Copy/paste the following command:
defaults write com.apple.finder AppleShowAllFiles YES
3. You now need to relaunch the Finder. You can do it…
… via Terminal by pasting this:
killall Finder
… or by holding down the option-key (⌥) then right-clicking on the Finder icon in he dock and choosing “Relaunch”.
To hide the hidden files and folders again, just repeat that process and replace the “YES” with a “NO”
For a more detailed look at this function and a neat trick to create a “shortcut/alias” please take a look at this article:
http://ianlunn.co.uk/articles/quickly-showhide-hidden-files-mac-os-x-mavericks/