I wanna change my dock

What do i use like a application or is there in Mac OS itself to customize it

What exactly do you want to do and are you running 10.4 or 10.5?

Try this: http://www.dockulicious.com/docks/index/page:1/

Download the dock you want. Than go to finder/hard drive/system/library/core services/dock...than right click "Dock" and choose "show package contents", than contents and than rescources. Scroll to the " scurve" dock icons and save them in a seperate folder somewhere on your computer. Than delete the old scurve icons from the resources file and add the scurve icons that you want from your download. You will probably have to authenticate it with your password each time you add one. After they are all added in the rescources file, go to " applications/utilities/terminal. Bring up the terminal and typer this exactly: killall Dock
Thats all there is to it...
Good luck and enjoy...