If your workflow requires that you take common screenshots on your Mac, you must know three keyboard shortcuts. Two of the three have been forever, and MacOS Mojave added a new screenshot tool and keyboard shortcut. Let's review your screenshots on a Mac.
It takes a screenshot of your entire screen.
It turns your cursor into a crosshair that you can drag to select a part of your screen to capture. Release the mouse button or touchpad to take the picture.
You have a number of other options after pressing Shift-Command-4:
Press and release spacebar : The cross becomes a small camera icon that you can move across all open windows. Click on the desired window to take a screenshot of it. A screenshot taken with this method has a white border around the window with a little drop shadow.
Press and hold the spacebar (after dragging to mark an area but before releasing the mouse button or trackpad): This locks in the shape and size of the selection area, but allows you to reposition it on the screen. It is very useful if your first selection area is turned off by a few pixels. Simply hold down the spacebar to place it before releasing the mouse button to capture a screenshot.
Hold down the Shift key (after dragging to mark an area but before releasing the mouse button or trackpad): This Lock on each side of the selection area made with the crosshairs, save the bottom edge, so you move the mouse up or down to place the bottom edge. Without releasing the mouse button, release the Shift key and turn it again to place the right edge of your selection. You can switch between moving the bottom edge and the right edge by holding down the mouse button or touchpad and pressing the Shift key.
MacOS Mojave introduced this hotkey. It rings a small panel at the bottom of the screen with your screen capture options. There are three screenshot buttons that let you capture the entire screen, a window or a selection of your screen. Similarly, the two recording buttons can record the entire screen or a selection of it. To the left is an X button to close the screen capture panel, but you can also just press the Escape button to exit.
On the right side there is a radio button. It lets you choose where to save the screenshot – Desktop, Docs, Clipboard, Mail, Messages, or Preview – and set a 5 or 10 second delay so you can arrange items that would otherwise disappear when you connect the screenshot utility.
By default, the Show Liquid Thumbnail option, which adds a small preview of the thumbnail for the capture image in the lower right corner of the screen, is similar to the screen dump procedure introduced with iOS 11 (and with which you areDo you own and operate a ). Unlike your iPhone, you can turn off this preview memory image on your Mac. Finally, you can choose to display the mouse pointer on a screenshot or video.
If the screen capture panel is on your way, grab the left edge and drag it to a new location on the screen.
If you embrace the floating thumbnail, you get quick access to Markup Utility to comment on your screenshot. You can swipe the floating thumbnail away or just let it slide away on your own and it will be saved to the place you last saved a screenshot. Click on the floating thumbnail and it will open in a Markup View preview window (but not preview) with all the selection tools you get in preview.  You can right-click on the floating thumbnail to:
- Save the screenshot to the desktop, document folder or clipboard
- Open it in Mail, Messages, Preview or Photos
- View in Finder
- Open in the Markup preview window as described above
- Close (and save)
Longtime Mac screenshots may be slow to assume the new Shift-5 shortcut command but I'm starting to use it more to annotate screenshots without having to open Preview and quickly delete screenshots that I know immediately I messed up. The 5- and 10-second delay options are also useful and estimated additions.
Originally published June 27, 2018.
Update, November 16: Add new information about all three MacOS screenshot keyboard shortcuts.