Windows 10 will, if an update has downloaded, enter a low-power-state when you press "Shut Down" and wait until when it thinks you won't be using your computer (you can manually set the time in the settings menu somewhere), at which point it will boot, install the updates and then completely shut down.
You can hold down shift while pressing "Shut Down" to force an update on Shut Down so that your computer will actually turn off.