How to take a full-screen screenshot
If you want to share what your entire desktop looks like, open apps and desktop files, and all, press command + shift + 3.
How to take a screenshot of a selected window
If you want to take a screenshot of a specific window that you have open on your desktop, select the window, then press command + shift + 4, and then press the space bar. When the window is highlighted, click your mouse or trackpad.
How to take a screenshot of a specific spot on the screen
If you want to take a screenshot of a specific spot on your screen, press command + shift + 4 and then click and drag the crosshair across the section you want to take the screenshot of. When you have the entire section highlighted, let go of the mouse or trackpad.
How to quit an app
If you want to close an app out completely, press command + q.
How to open a new tab
With macOS Sierra, any window can have a tab. Not all apps support multi-tab controls, but for ones that do, press command + t to open a new one.
How to switch between open apps
Apple has an application switcher that makes it easy to switch between open apps at a glance, press command + tab to open it. Then press left arrow or right arrow to switch between open apps.
How to open an app’s Preferences window
The Preferences window is where you can find many of an app’s tools and special features. You can call up the Preferences window by pressing command + comma.
How to open Spotlight
If you’re looking for something, either on your Mac or on the web, call up Spotlight to help you dig through it all by pressing command + space bar.
How to open the Help menu
If you are trying to troubleshoot your Mac, or find out more about what an app can do, press command + shift + ?.
How to force-quit an app
If the app you are using freezes up or stops responding, you can force it to close by pressing command + option + esc.
How to cut, copy, paste, and undo
When in a document, email, message, or other program where you can type text, you can cut, copy, paste, or undo by pressing command and then X, C, V, or Z respectively.
How to find words and phrases in a document, web page, or other app
You can quickly find and highlight words and phrases in any app that support the Find feature by pressing command + f.
How to launch Quick Look
When searching for a specific document in Finder, you can use Quick Look to get a preview of a file’s contents by pressing command + y. You can also select the file and press the spacebar.
How to shut down, sleep, or restart your Mac
If you are ready to walk away from your Mac, and it’s time to put it into lockdown, you can put it to sleep, shut it down, or restart it by pressing control + eject.
If you have no eject button than follow this Shut Down: Control-Option-Command-Power, Mac to Sleep: Option-Command-Power, Display to Sleep: Control-Shift-Power
How to select all
If you want to copy and paste an entire page of a document, press command + a to select all.
How to jump to the top or bottom of a page
If you are viewing a long document or web page, you can quickly jump to the very top or very bottom by pressing the command + arrow up or arrow down.
How to hide windows you aren’t using right now
If you want to keep your desktop free of clutter so you can focus on the task at hand, hide windows you aren’t using by pressing command + h. All apps except the topmost one will disappear. Click on the app’s icon to bring it back into sight.
How to minimize a window
If you just want to get a window out of the way for a moment, you can minimize it by pressing command + m.
How to close an active window
If you don’t want to quit an app completely, but want to close the currently active window, press command + w.
How to close all windows of an app
If you are done with an app and want to close all windows you have open and lying around, press command + option + w.
How to hide or minimize everything on your desktop
If you want to quickly clear everything so that only your desktop is showing, press command + h + m and all windows of all apps will either hide or minimize.