It's known for a relatively steep learning curve - because there are an unbelievable number of options for VI, but you can get by with a few basic commands (see below for the cheatsheet).
=== VI Improved ===
On modern systems vim is actually the package that is installed because it succeeds the predecessor 'vi' There are many other vim-related packages. Check if vi is a symbolic link to vim (<code>file `which vi`</code>), and if not then <code>sudo apt-get install vim</code>.