Enter Insert/Edit Mode

# enter insert mode, can edit file content
i

# switch back to the command mode from insert mode
esc

Undo/Redo

# Undo last action
u

# Redo last undo
ctrl + r

Copy/Cut/Paste

# Copy selection
y

# Cut selection
d

# Paste selection (in line)
p

# Paste selection (line above)
P

Delete lines

# Delete current line while in command mode
dd

# Delete current line without overriding yank
_dd

# Delete 3 lines while in command mode (n-number of lines)
3dd

Swap Lines

# Swap current line with line above
ddkP

# Swap current line with line below
ddp

Indentation

# Indent selection (tab) in visual mode
>>

# Unindent (shift + tab) in visual mode
<<