Can you be more specific?
To edit any theme file, you’ll need to open up the page in a code editor or text editor and edit it. You’ll need to understand some HTML and ideally some PHP in order to edit these files effectively. (There is also a way to edit these files within the WordPress interface, but I never recommend that method as it’s much riskier than editing a local copy on your own computer first.)
I need to know what the bits of code mean. Basically.
Check out this article:
Understanding WordPress Theme
http://maketecheasier.com/understanding-wordpress-theme/2010/01/07
It walks through some of the major theme files bit by bit. It’s not completely current but should start to give you a sense of what’s what.