how to i create a folder under root?
 

whats the command?

mkdir makes a folder...what exactly do you mean by "under root"? try typing su and your password first

ok, thx

Here is a list of commands with description.
http://www.oreillynet.com/linux/cmd/

The list is long and most of them you will most likely never use.
But it is a good online reference table. :)