ImageChooser Source Help - Ext JS

I have been trying to learn the basics of Java OO. I have read the wiki post on the subject and hve gone throught he many links on that page (and I will continute to read and absorb the info).

After some reading I have been going to Jack's examples and I have some questions about the ImageChooser.

Two lines have my interest:

var ImageChooser = function(config){
ImageChooser.prototype = {

Can someone help explain the purpose of each (maybe contrasting them)? I have a vague idea but I could use someone elses perspective.

Thanks for any help.