The Dock is in my opinion one of the best features of OS X but it doesn't come with any alternative templates and styles.
That's where Dock Library steps in to provide you with several different templates and looks for your dock which can be activated in a click. Once you have installed Dock Library, you're presented with the main selection window where you can choose which Dock to activate. The problem is, it's empty so you'll need to download some styles from LeopardDocks.net or LeopardDocks.com. The styles are in zip format but you don't have to unzip them - just upload them to Dock Library and activate them.
There's not much more to Dock Library than that. The top dock in the selection list is always the default one so you can always undo any changes by selecting it. Changes are immediate although you may have to enter your Mac user password. There are no preferences other than whether to choose to check for updates on startup.
It would have been nice to have the styles preloaded into Dock Library by default without having to download them but that doesn't take away from the fact that it's a great little customisation tool.