template editing

newbie: I just installed wordpress. I need to change the layout of the default page. I’ve been looking at documentation, but am duly confused a bit here. When I open the admin panel of wordpress online, I see I can edit index.php. What I think I need to edit is the css file, wp-layout.css – which is referenced in index.php — correct? I don’t see any way to get at the css file on the on-line editor. I guess for modifying the blog page it is necessary to edit both the index.php and the wp-layout.css, depending on what is being altered, correct? Help is appreciated!