But if you try that right now, it won’t work. First, you need to fire up Terminal and paste in this command:
defaults write com.apple.dock double-tap-jump-back -bool TRUE;killall Dock
The first part of that command enables the double-tap jump-back setting; the second restarts the Dock, which puts that change into effect. To try out your new gesture, swipe to the right with four fingers to reveal the Dashboard, and then double-tap with four fingers to come right back here again.