And it helped me to remember that the old filename goes away.
Here's an example:
I want to rename OldFile to OldFileNewName.
So I type mv OldFile OldFileNewName
then when you do an ls of the directory, 'OldFile' is gone, and 'OldFileNewName' has taken its place.
Probably redundant for you, but I thought I'd share....
Katy