What is the difference between a tap and a click?
According to this article: Turning On Mac Touch-To-Click Support from the Command Line you have to enable the feature in the command line:

Enable the general tap-to-click behavior:

sudo defaults write com.apple.driver.AppleBluetoothMultitouch.trackpad Clicking -bool true


Enables tap-to-click for the Magic Mouse:

sudo defaults -currentHost write NSGlobalDomain com.apple.mouse.tapBehavior -int 1


Enable tap-to-click at the login and boot screens of OS X:

sudo defaults write NSGlobalDomain com.apple.mouse.tapBehavior -int 1


and reboot your Mac.

To disable all this enter in Terminal:

sudo defaults write com.apple.driver.AppleBluetoothMultitouch.trackpad Clicking -bool false
sudo defaults -currentHost write NSGlobalDomain com.apple.mouse.tapBehavior -int 0
sudo defaults write NSGlobalDomain com.apple.mouse.tapBehavior -int 0


and reboot again.