Explaination of where images, css, etc are stored

I want to start changing the template to fit my design.  There are so many elements between the images, css pages and php pages.  Is there some easy documentation where I can quickly find out where to alter the look of each element?  For example, a screenshot of the default template and arrows showing where each image, element, menu, etc is stored or what they're called?

Thanks

I suggest you use Firefox with the Firebug extension installed, which lets you quickly and easily find the needed segments of code for web sites.