Question : PHP in Joomla

Hello All,
I want to know is it possible to edit php in Joomla?If yes then how?Can I get how is it running query's for entering data in database etc?Is there a tutorial for it,or any documentation?
Thanks

Answer : PHP in Joomla

You might find it helpful to look at Joomla plug-ins.  This may be better than editing the code yourself, since you will probably want to upgrade your Joomla installation some day, and edited code will be a new adventure with every release of Joomla!