That's the stud pattern, offset is how much they'll stick out depending on how deep the mounting face is on the wheel, it's usually stamped on the inside of the wheel and is a 2 digit number shown as et**. As Buckz says wheel width is also important, should also be stamped on the back of the wheel as 8j, 9j etc for inches in width.
Reading this should help you;
http://www.rimstyle.com/pages/alloy_wheels_explained.html