$ vi file   # open file
:w          # save (write)
:wq         # save and quit 
:x          # abbreviation of wq
:q!         # quit without save

h           # cursor left
j           # cursor down
k           # cursor up
l           # cursor right
0           # (zero) move to beginning of the line
$           # move to the end of the line
w           # move to the beginning of the next word
}           # skip to next section
H           # Jump to the beginning of the displayed screen
M           # Jump to the center of the displayed screen
L           # Jump to the bottommost line shown
CTRL-f      # Jump down one Page
CTRL-b      # Jump up one Page
CTRL-d      # Jump down halve a page
CTRL-u      # Jump up halve a page
gj          # For very long lines that wrap at the screen edge, jump up one line.
gk          # For very long lines that wrap at the screen edge, jump down one line.
%           # Jump to the next bracket character (){}[]

i           # insert at cursor position
a           # add after cursor position
o           # insert a line below
O           # insert a line above
12i <character>   # write the same character 12 times  ( type eight zero i dash <ESC> results in ------------)
y           # yank text (copy)
d           # delete
dt'         # delete everything to the character '
df'         # delete everything including character '
c           # copy line
y$          # copy to the end of the line (yank)
y5l         # yank five Characters from the cursor position to the right
yt(         # copy everything to the round bracket
d2w         #  delete two words
c2j         # change the next two lines
:undo or u
:redo or CTRL-R

CTRL-q       Cursor turns gray as soon you move the cursor keys (or hjkl). Mark everything you want comment
SHIFT-i       press Shift Key and i
#                  type '#'
ESC             Press ESC

Add '# ' in the beginning of line 5 to 12

:5,12s/^/# /     

CTRL-q     Mark everything you want to remove
q             press q

remove '# ' from the beginning of line 5 to 12

:5,12s/^# //