Blog Facing Probs

Yeah... haven't been bloggin cos' I couldn't get to my latest post when I click the url http://som2550.blogspot.com... have to ask Eve to give me the url she always go to so I can try her link: http://www.som2550.blogspot.com and walla! It worked! HMM.. but whats the diff with the "www" ? I have always been using the link without. hmm...