Modern browsers display RSS feed with their own styling and so far it is not possible to override the display format they use , but yet some browsers like internet explorer 6, does not use any custom style for displaying RSS feed, rather you will see the bunch of raw xml data on your page which is not at the least reader friendly.
So , to show feeds from our websites in a nice way with a better look and feel and surely with some branding ( like a logo with the feed list ), what we can do is to add CSS over it. But the problem is , if only CSS is used , the links are then not clickable, so you cannot go to the original news or article by clicking its title. Here comes the need for using XSL transformation. By using xslt, you can convert the raw xml file with feedlist to a nice looking page with custom design - this is how actually the browsers like firefox and IE7 do it.
Foe beginners , to learn about xslt: http://www.w3schools.com/xsl/