Tapping the mousepad doesn't click
There's good reason for this. By default, the mousepad no longer clicks. The reason is that the problems this can cause with unintentional clicking (clicking when you don't want to click). If you want this behaviour, it's not too hard to put it in.
Click on the Ubuntu symbol at the top left of the screen.
Click on System. This is where you can make all sorts of changes to the system.
Look for the touchpad icon as shown in the image below. Click on this.
Select "Tapping" from the menu at the top of the window that appears.
You should see the screen shown below. Click on the "Enable Tapping" checkbox.
Click on Close.