Mac OS: Cut, copy, paste, and other common shortcuts:

Cmd + c              : Copy the selected item to the clipboard. 
                       This also works for files in the Finder.
Cmd + v              : Paste the contents of the clipboard into the current document or app. 
                       This also works for files in the Finder.
Cmd + x              : Cut the selected item and copy it to the clipboard.
Cmd + a              : Select all items.
Cmd + z              : Undo the previous command. 
                   
Shift + Cmd + Z      : To Redo, reversing the undo command. 
                       In some apps, you can undo and redo multiple commands.
                   
Cmd + f              : Find items in a document or open a Find window.
Cmd + g              : Find Again: Find the next occurrence of the item previously found. 
Shift + Cmd + g      : To find the previous occurrence from last shortcut.
Cmd + h              : Hide the windows of the front app. 
Option + Cmd + h     : To view the front app but hide all other apps.
                     
Cmd + m              : Minimize the front window to the Dock. 
                     
Option + Cmd + m     : To minimize all windows of the front app.
Cmd + s              : Save the current document.
Cmd + o              : Open the selected item, or open a dialog to select a file to open.
Cmd + p              : Print the current document.
Cmd + t              : Open a new tab.
Cmd + w              : Close the front window. 
Option + Cmd + W     : To close all windows of the app.
Option + Cmd + Esc   : Force quit an app.
Cmd + space bar      : Show or hide the Spotlight search field. 
                     
Command + Option     : To perform a Spotlight search from a Finder window. 
+ space bar            If you use multiple input sources to type in different languages
                       , these shortcuts change input sources instead of showing Spotlight.
                       
                        
                     
Ctrl + Cmd           : Show the character viewer, 
+ space bar            from which you can choose emoji and other symbols.
Cmd + Comma (,)      : Open preferences for the front app.
        
Ctrl + Cmd + f       : Use the app in full screen, if supported by the app.
Command + Tab        : Switch to the next most recently used app among your open apps.
 
Shift + Cmd + N      : Create a new folder in the Finder.
 
For more information, see here.
 
 
Taking a screenshot shortcuts:
1. Entire screen: Cmd + shift + 3
You will find screenshot on your desktop. It will be saved as 'screenshot' labeled with the date and time.
 
2. Screenshot a portion of your screen: Cmd + shift + 4
Click and drag your cursor to highlight the area you'd like to take a picture of, and release mouse.
Tip: to maintain resolution when you email the image make sure you send it as actual size or close to it:

 
For more information, see here.