Coding questions., advanced or am I behind? Options

[Genocide]

A few questions about coding:

I understand what padding does, but what does it do when you have more than one pixel amount side by side?

CODE

padding: 2px 4px;

In this layout http://www.createblog.com/layouts/code.php?id=28124 what does this part of the code for the navigation links do?

CODE

-moz-box-sizing: padding-box;

or this

CODE

margin: 3px 2px;