So far is i now you can make custom.css in the Css folder and is it not there you can create it there.

after creating custom.css in css folder.......... how to load the module with its own stylesheet.......... can you explain me code thanks

Hi Sumit,

I am not sure understand what you want.
1. Create a custom.css file in template 'css' folder, and it will be load automatically (please do not modify the head.php, there a rule to load custom.css file in this file).
2. A module can/should have their stylesheet. Just use official "JDocument"->addStylesheet method to add your stylesheet for module.
3. You can always add any other style sheet by modify head.php, you can use addStylesheet via PHP code or <link .../> tag

Hope it clears

Regards

@Sumit
As "Super User" said, you can add it to the head.php file.

The head.php file is located in <site root>/templates/t3_blank/tpls/blocks/header.php