Multiple lines comment and uncommnet in VIM

To comment out blocks in vim:

• press Esc (to leave editing or other mode)
• hit ctrl+v (visual block mode)
• use the up/down arrow keys to select lines you want (it won't highlight everything - it's OK!)
• Shift+i (capital I)
• insert the text you want, i.e. %
• press EscEsc

To uncomment:

Put your cursor on the first # character, press CtrlV (or CtrlQ for gVim), and go down until the last commented line and press x, that will delete all the # characters vertically.

Duplicating a line in Vim Eiditor

yy or Y to copy the line 
or 
dd to delete (cutting) the line

then

p to paste the copied or deleted text after the current line 
or 
P to paste the copied or deleted text before the current line