How to take a screenshot on Samsung's Galaxy S9, S9 Plus and Note 8

It's the simplest thing in the world: to take a snapshot of your screen and share it with someone, but how do you do it on the Samsung Galaxy S9 series and on the Note 8?

Samsung being Samsung, there is more than one way to do it, but let's start with the universal shortcut that works on many other phones as well: 

1. simply hold down the power key (the one on the right) and the volume down key (on the left) simultaneously for a moment

and you will hear a shutter click and will see your screen pop at you indicating that a screenshot ...