[ubuntu-za] ubuntu command language

[Robbie Holm]

I am a complete newcomer to linux, and have loaded Ubuntu.
How do I begin to learn about the command line language?
The only book I have been able to find is "Linux For Dummies" but this 
deals specifically with Red Hat, SUSE and Knoppix.
Are the commands in these different versions and Ubuntu identical?
Naturally I don't want to spend money on something that will not be useful.
Advice would be greatly appreciated.

Robbie Holm.