Note: Cmd looks like "⌘" on the keyboard.
Cmd+C: Copy selected text or item
Cmd+V: Paste copied text or item
Cmd+X: Cut selected text or item
Cmd+Z: Undo last action
Cmd+Shift+Z: Redo last undone action
Cmd+Tab: Switch between open applications
Cmd+A: Select all items in a document or window
Cmd+P: Print current page or document
Cmd+F: Search or find within a document
Cmd+S: Save current document
Cmd+O: Open a file
Cmd+W: Close current window
Cmd+Q: Quit the application
Cmd+Opt+Esc: Open Force Quit Applications window
Cmd+Space: Open Spotlight Search
Ctrl+Cmd+Q: Lock your computer
F11: Show Desktop
Cmd+Shift+4: Take a screenshot of a selected area
Cmd+Shift+3: Take a screenshot of the entire screen
Cmd+T: Open a new tab in a browser
Cmd+Shift+T: Reopen last closed tab in a browser
Cmd+Left Arrow: Go back one page in a browser
Cmd+Right Arrow: Go forward one page in a browser
Cmd+R: Refresh current application or webpage
Cmd+Shift+[: Move backward through tabs in a browser
Cmd+Shift+]: Move forward through tabs in a browser
Cmd+M: Minimize the front window to the Dock
Cmd+Opt+H: Hide all other windows
Cmd+I: Show Get Info window for a selected file
Cmd+Shift+N: Create a new folder