Show line numbers:

:set nu

“Unshow” line numbers:

:set nonu

Add show/unshow line numbering in vim (F12 key) Add following to /etc/vimrc

nmap <F12> :set number!<CR>

Current line = .

Insert comment character on current and next 5 lines:

:.,+5s/^/#/g

Change all appearances of from to morf from line 1 to current line:

:1,.s/from/morf/g 

Mark the area which is to be commented using the *blockwise* visual mode (CTRL-V)
Press I (capital i) and write the text you want to prepend to each line of the selected block, e.g. %.
Then press ESC and the text will be inserted to the left of each line of the selected block.

Shift + v