[development] Style's stuff

[Gustavo Cabral]

Hello everyone:
I need to change the look of certain pages, ie I have installed the
organic group, and only I want to change the appearance of any content
generated by this module with CSS. How can I differentiate them from
other content?
I know I have to change or rename the file page.tpl.php, but I do not
know what I need to put as file name.
I am a rookie in styles, forgive me.
Thank you very much. I appreciate their support.

Gustavo .-