How to define a variable?

[Mauricio]

Hi all,
as you can see, I'm starting with SB. I saw in the examples (dialog2, for example) a dialog window for a password that save the result in a variable (%_SB_PASSWORD%). I looked for in the script but I couldn't find where that variable is defined.
I read the help too but I didn't find anything.
So, any help will be appreciated.
Thanks in advance.

Mauricio