daftduke - thanks for providing that snippet to hide the footer credits.
However, you can view the template files inside the dashboard by going to
Appearance -> Editor
I don't recommend that you edit the theme files directly, otherwise your changes will be overwritten whenever the theme is updated, and you'll lose all your changes.
An easy way to add custom CSS is to install the Jetpack plugin and activate the Custom CSS module. You'll then add your custom CSS in the new stylesheet editor that'll appear in your dashboard, under Appearance > Edit CSS.
As an alternative, you could install a standalone custom CSS plugin.
If you decide to go the more advanced child-theme route - usually only needed if you have more than just CSS changes to make, such as tweaks to template files - here are some guides:
http://codex.wordpress.org/Child_Themes
http://op111.net/53/
http://vimeo.com/39023468