A cheat sheet I have produced while learning how to use the almighty editor

Esc - Normal Mode (default)
i - Insert Mode
(modifier)v - Visual mode
R - Replace mode (just like hitting the Insert key on the keyboard)

h - left
j - down
k - up
l - right

0 - go to the beginning of line
$ - go to the end of line

w - go to beginning to next word
b - go to beginning of previous word
e - go to end of next word

{ - go to previous paragraph
} - go to next paragraph

% - go to matching parenthesis/bracket

i - insert before current Char
I - insert before current line

a - append after current letter
A - append at the end of current line

o - insert starting at a new line after the current one
O - insert starting a new line before current one

r - replace current char with another

cc - delete current line and enter insert mode
cw - delete current word and enter insert mode
c$ - delete until end of line and enter insert mode

x - delete current char
X - delete previous char (backspace)

dd - delete current line
dw - delete a word (from cursor)
diw - delete a word (from beginning of word)

d$ - delete everything until the end of line
d0 - delete everything until beginning of line

y - yank (copy)
yy - copy line
yw - copy word (from beginning of cursor)
yiw - copy word (from beginning of word)
y (during visual mode) - copy highlighted text

p - paste the yanked buffer

. (dot) - redo previously performed command
u - undo previously performed command

>> - indent line
<< - reindent line

/ - forward search
? - backward search

n - go to next found occurence
N - go to previously found occurence

%s - sed through all file
{num},s - sed from {num} line forward
,{num}s - sed from beginning of file until {num}
{num1},{num2}s - sed from {num1} line to {num2} line

format: {range}s/{search-term}/{replace-term}/{options}
NOTE: {search-term} can be regex

possible {options}:
g - match multiple times on a single line
c - ask before replacing

:!{external command} - executes command and returns to vim after execution
:r!{external command} - read the result of external command and put it under cursor
:{num1},{num2}! {command} - replace the contents of the file between line {num1} and {num2} with result of external command.
Feed as input the contents between those lines.

:q - quit without saving
:w - save without exiting
:x - save and exit
:saveas {file} - save changes to {file}

ZZ - save and exit

Every command can be performed several times by supplying it with a number

e.g. 4iHello There\n results in:

Hello There
Hello There
Hello There
Hello There

Similarly, you can do the same for shortcuts such as [x, u, r...].
The only exception is the d shortcut (delete).

For it, you have to supply the number after the command. Also, you have to specify a direction for deleting by using the arrow keys.

e.g. d4(right) will delete the next 4 characterx starting from the cursor.

e.g. d4$ will delete the next 4 lines.