Step 1: Open Terminal.
There are 2 ways to open Terminal:
Method 1: From Desktop (Finder), Go -> Applications -> Utilities -> Terminal.app
Method 2: Using hotkey to open Spotlight (Command + SpaceBar is default), type “Terminal” then press Enter to open up the Terminal.
Step 2: Copy this following line and paste it to your Terminal:
defaults write com.apple.finder AppleShowAllFiles YES
Step 3: Relaunch Finder to see effects.
We also have 2 ways to do this step:
Method 1: Holding “Option/alt” on keyboard and right-click on “Finder” icon on the dock, choose “Relaunch”.
Method 2: Run this command from Terminal: killall Finder /System/Library/CoreServices/Finder.app
To rollback to default setting (DO NOT show hidden files/folders), just replace YES to NO on the step 2.