someone can tell me how can i improve CMS platforms like joomla, wordpress.i know something about worpress but i don’t know how to work php in worpress.
Hi shakir90. Welcome to the forums. 
To be able to manipulate how these CMSes work, you’ll need to learn some PHP.
Get a free plugin and check how it works. Same things with themes.
i have worked php in my localhost. I can make a registration form with php, if i entry my database information like name, usear name, password that,s informatin saved in mysql database. But my qusetion how can i make a registration form in wordpress and that,s information save in mysql database.
Yes, as noted, there are lots of add-ons for WordPress and other CMSes for this sort of thing, such as
If none of the available add-ons does what you need, you could look at how they are made and modify them or build your own if you are good enough at PHP.
I think these links might get helpful to you.
for Wordpress
http://www.wordpressninja.com/2011/02/the-ultimate-guide-to-use-wordpress-as-a-cms/
for Jooml
http://docs.joomla.org/Beginners
http://docs.joomla.org/
http://help.joomla.org/
for Magento
http://www.magentocommerce.com/resources/magento-user-guide
http://www.magentocommerce.com/design_guide
These might be useful to you…