hi i want to replace a module with another in magento how can i do this (means i want to put Community Poll module to the left ) is there anything like joomla im a newbie in magento so plz be descriptive with your answer
Have a look in app/layout/default/default/layout - you should be able to swap a value out in the XML there to cause a different block to be displayed.
I'll try and remember to look in more detail when I've got a dev copy of magento to hand and will update the answer.
The layout is defined in XML files.
Read this to understand the basic philosophy and this for a crash course in changing the layout.
As already mentioned, the layout is defined in the XML files. The best way to go about it is to search the layout folder in App/Design/Frontend/Default/whateverthemeyouareusing for the names of the blocks you want to re-arrange. You'll find there might be more than one call for a block. They will have a position stated in the reference name, either left or right, and can also be before or after another module. Changing these values will move the blocks around.
For example:
< reference name="left">
< block type="catalog/navigation" name="catalog.leftnav" after="currency" template="catalog/navigation/left.phtml"/>
< /reference>