The documentation has already covered this. If you have any specific questions, feel free to edit your main post.
Official:
- Page Objects and PageFactory on Selenuim Wiki.
- Page Object Design Pattern on Selenium official site.
Unofficial:
Do a Google search, you will get a lot info on this.
- Page Object Pattern
- Page Objects in Selenium 2.0
- Selenium 2/WebDriver Quick Tips: Page Object Navigation Strategies
- PageObject by Martin Fowler