Here is list of basic commands to work on Vim editor in unix environment. Hope this would help new learners and people preparing for interviews.
Best way to learn these commands is using -
vimtutor
go to unix shell and type command vimtutor. Follow instructions on this tutorial and practice it hands-on.

Start Vim

vim [filename]

To start Vim from shell prompt

Exit Vim

<ESC> :q!	exit without saving changes
<ESC> :wq	saving changes and exit

<ESC> key is used to return to normal mode. (you might be in editing mode)
Move Cursor

h	left
j	down
k	up
l	right

Motions

w	first character of next word
e	last character of next word
$	last character of line
move faster -
0 (Zero)	To move to start of line
nw e.g. - 2w	Move forward by n words (e.g. - 2 words)
gg	move to start of the file
G	move to bottom of the file

Undo

u	undo last command
U	undo changes on whole line

Delete character, word, Line

x	delete character at cursor
dw	delete word, including last character (place cursor on first character of word)
de	delete word, excluding last character (place cursor on first character of word)
d$	delete words from cursor position till end of line
dd	delete line
delete more -
nd[motion] e.g. - 2dd	delete n lines from cursor position (e.g. - delete 2 lines)

Insert and Append text

i	insert before cursor (press <ESC> after, to return to normal mode)
A	append after the line (press <ESC> after, to return to normal mode)

Search

/[phrase]	search pharse in file
n	go to next match
N	go to previous match

Replace/substitute

s/old/new	on current line, substitute first occurence of old with new
s/old/new/g	substitute all old with new on current line
%s/old/new/g	substitute all old with new in file
%s/old/new/gc	substitute all old with new in file, ask for confirmation

These are few basic commands to begin and practice.
Please leave your comments here and let us know if this helps.