General Commands:
To exit vi and save changes: ZZ or :wq
To exit vi without saving changes: :q!
To enter vi command mode: [esc]
Inserting
r replace character under cursor with next character typed
R keep replacing character until [esc] is hit
i insert before cursor
a append after cursor
A append at end of line
O open line above cursor and enter append mode
:%s/original/replacement Replace original text with replacement text
:%s/original/replacement/g Replace all (/gc with confirmation)
Deleting
x delete character under cursor
dd delete line under cursor
dw delete word under cursor
db delete word before cursor