Enter insert mode:

i

In insert mode, you can type and insert text as you are used to with most other text editors.

Insert text after current character:

a

Move to the beginning of the document:

gg

Move to the end of the document:

G

Move to the top of the screen:

H

Move to the bottom of the screen:

B

Move to the middle of the screen:

M

Move one full screen forwards:

 f

Move one full screen backwards:

 b

Move one half screen forwards:

 d

Move on half screen backwards:

 u

Move to the beginning of the current line:

0

Move to the end of the current line:

$

Delete character forward:

x

Delete character backward:

X

Delete entire line of text:

dd

Delete n lines of text (n is any positive integer):

n dd

To change the current word:

cw

To change the current letter:

cl