Docking in Macbook pro

I have just started using a macbook pro after using windows for a few years. My question is , How can you add and remove apps from the docking system at the bottom of the desktop? I am using the OX Lion update that has recently been out

It's just called the Dock.

Remove items from the Dock by grabbing it with your cursor, drag it off the dock and release. It will disappear in a puff of smoke. Or, you can right click the icon, go to Options and select Remove from Dock. This does not delete or do anything else except remove it from the Dock.

To add items to the Dock - while you have the app open, you can right click on it's icon - Options - Keep in Dock. Or, you can open Finder and drag the app icon from your Applications folder and drop it into the Dock.

Thanks as you can probably tell I'm new to a Mac I think once I get used to it it looks as if it'll seem a bit easier than the Linux I was using just after I finished using windows. Oops there is one more question, I downloaded an extension called 'twitter for safari but dont know how to find extensions in Safari and operate it? Thanks again.