SermonSpeaker uses CSS (Cascading Style Sheets) for many things. If you want to change stuff like the background color of the table rows or the font color of the download button, you may want to look at the CSS definition file located in /media/com_sermonspeaker/css/sermonspeaker.css.
Of course this is not the only place where CSS is applied, the most important one is coming from your template. This one could be edited directly in the Joomla Backend Template Manager.

If you're not sure why something looks like it does, you could use tools like Firebug Addon for Firefox or the built-in tools of IE and other browsers (usually opened with F12) to see what CSS gets applied to a given element.

If you're not familiar with CSS I suggest that you google it up, there are famous guides out there in the web. And CSS isn't hard to learn, but it allows great ways to customize your site without touching the code at all.

If you're a bit more hardcore and want to edit the HTML itself, you may want to look at the template file for a given view. You find them in /components/com_sermonspeaker/views/view-name-here/tmpl. They contain more or less plain HTML with PHP tags ( between. You can edit the HTML as much as you like, as long as you contain the PHP tags untouched. You may move the PHP tags or even delete some of them, but you should not edit them if you're not sure what you do. You can read more about layouting in SermonSpeaker in the layouting documentation.
If you create a new nice layout, I'm more than happy if you send it to me so I could include it in the next version of SermonSpeaker. It's opensource software after all :-)