Select the text, file, or item you want to copy
Press Command + C to copy
Click where you want to paste
Press Command + V to paste
To cut instead of copy, press Command + X
To paste without formatting in some apps, press Shift + Option + Command + V
You can also right-click and choose Copy or Paste
On a trackpad, use two-finger click to open the context menu
In Finder, you can copy files with Command + C and paste them with Command + V
To duplicate a file in Finder, press Command + D