Taking a take a screenshot has always been the same on all older iPhones, but with the removal of the Home button from the iPhone X. If you have never owned an iPhone X or later, but have now the new iPhone 11 or iPhone 11 Pro, this is what you need to do.
All you have to do is to press the Volume Up and power/side button simultaneously. A screen will then be acquired and a preview will appear at the bottom of the screen.
If you simply want to save the screenshot, you can scroll through the preview; otherwise to edit the screenshot, simply touch it and you will be taken into edit mode.
Once in edit mode, you can then share the image or edit it. There are many different changes you can make, including cropping and even drawing arrows.