How to do defragment disk on Mac?

Please help, I'm a dummy for Mac. This is my first time that I use Mac System. I've tried "help" on tool bar and even bought a book "Mac for Dummies" but I could not find any help regarding to "Disk Defragment". If any members know how to get Disk defragment work or locate its icon please show me how to do or get it. Thank you very much.
Here's the official word from Apple on defragmentation. What they say, essentially, is that with OS X there's not much to be gained by doing it unless you do a lot of video editing. If you do decide you need to do it you'll have to use a third-party utility.
One of the beauties of a Mac is that you don't ever need to defragment the disk. I'm pretty sure there's some facility to do so, but you probably don't need to concern yourself with it.

Welcome to the bright side.

Use the procedure testing and repairing a disk or volume. This information is located under disc/utility located in the applications/utilities. Follow the four steps described. By the way always use the help menu to located information about the MAC it will save you a lot of time.
I believe the Mac OSX is similar to most Linux file systems. It does not need to be defragmented in the same manner that Windows systems need. File maintenance is not required in the same manner and whatever is needed generally takes place in the background.
Norton Utilities and Techtool Pro are third party applications for Macs. Cocktail (10 day free trial) can be used for cleaning caches, optimizing ect. Or just launch Disc Utilities choose the disc you want to check and follow directions.
As the above but also remember to both leave your Mac on over night and/or turn it off occasionally. The computer does some maintenance scheduled at night, and at start-up (see Mlsstl and the reason for restart advice from the Sfar link).
There is another Mac utility called MacJanitor, it cleans up the disc without having to leave your computer on all night.

You can download it here for free.

One more suggestion, especially if you run any Microsoft applications on your mac or do file sharing.

Download Peer Guardian and it will block attempts at spying from government, Edu, Internet providers, Spyware, Microsoft Corp and others.

It too is free. I've had file sharing sessions where as many as 2 thousand hits were made on my computer, all turned away by this free application.
Another exceptionally useful Mac utility is MainMenu. It runs all the routine maintenance scripts that Albert mentions plus lots of other useful tasks like rebuilding your Spotlight index, repairing disk permissions, clearing caches and histories and removing temporary files, all from a single icon in the menu bar.
First of all, I would like to appreciate all members' information and knowledge. Second, I wanted to say thank all very much. Thanks again gentlemen.
I second it: Thanks guys!!!