How do i enable the compiz effects...?

If you want to use a pretty nice front end, install "fusion-icon" package & run it from Applications->System Tools->Compiz fusion icon.
use settings manager to set all available settings.

Also check these packages are installed for compiz to run in best way. (Use synaptic package manager for easy installation instead of apt-get install).
-compiz
-compiz-plugins-main (primary well tested plugins)
-compiz-plugins (standard plugins)
-compizconfig-backend-gconf (for gconf backend settings manager)
-fusion-icon (As stated above for settings management & changing window manager)
-compiz-gnome (gnome window manager if you are using ubuntu-gnome (if you are using kde version install "compiz-kde" instead))

Also install "compiz-plugins-extra" for advanced plugins and themes. These effects are not surely bug free. But I am using many of them & havn't found any big problem in it. And I think you probably want many of these effects.

When you run compiz fusion icon, make sure you select these in right-click menu.
select compiz from "select window manager".
& then click reload window manager for restarting window manager if something goes wrong or compiz is not started.

Do i need any graphics driver

Yes, of course you need graphic driver for your hardware to run these effect with highest performance.
Install the driver & restart compiz if you have already installed compiz prior to driver.
Can you give me the details of your graphic card?

Ok sir..
Ati radeon xpress 200 series
memory:256 mb
shader model: 2.0.

Just install driver from ubuntu software center named "ATI binary X.org Driver".
If it does not work go & install driver from this page. I have personally checked your hardware & driver is available both for 32 & 64 bit versions.
http://support.amd.com/us/gpudownload/Pages/index.aspx

After you install driver install compiz packages ( if not installed already ). Restart & enjoy.
Be sure to enable proper support for Gnome/KDE compatibility according to your ubuntu version (or else some specific shortcuts won't work).

hmm.. i try this that driver is in .run format. ubuntu does not recognize that format. say me another way. thx in advance

Have you try install driver from ubuntu software center named "ATI binary X.org Driver"???
If not try it. It's the simplest method to install without much trouble.

If you still want to install manually(a bit complicated method), follow the instructions on the website under.
https://help.ubuntu.com/community/BinaryDriverHowto/ATI
Follow it step by step to get it installed properly.

Yeah i tried that when i install the ubuntu for the first time.i think that compiz is not compatable with my computer.