This shortcut key is used in command-line mode:
I means go into edit mode and operate at the cursor location.
YY Copy the contents of the line where the cursor is
5yy the contents of the next 5 rows, including the line where the cursor is copied
P (lowercase) paste to the next line of the cursor
P (uppercase) pasted to the previous line of the cursor
3p Paste as many times as paste 3 times
DD Delete/Cut the contents of all rows of the cursor
3dd means to delete the contents of the next 3 rows, including the cursor.
DG Delete content from the line where the cursor begins to the end of the file
O (Small letter O) Insert a blank line below the line and enter edit mode
O (capital letter O) Insert a blank line above the current line and enter edit mode
C (capital letter C) Delete the cursor position to the end of the line and enter edit mode
A quickly arrives at the end of the line and enters edit mode
Vim's frequently used shortcut keys