Allows you to enter commands. To enter type :. This is technically a mode, but I thought it important enough to be a full subject.

Useful things to do in command mode:

• :w: Write. Save file.
• :q: Quit
• :wq: Write and then quit
• :!q: Force quit. Lets you quit without saving.
• .: Repeat last command
• :s/FIND/REPLACE/g: Find an replace text on current line
• :%s/FIND/REPLACE/g: Find an replace text in entire document