learn wordpress

hi,
Dears i want to learn wordpress and i confuse about theme design and plugin development.
what should be the first step. theme design or plugin if i want to be expert in wordpress

 

You will need basic knowledge in PHP first, i would go with theme customization and design first and once you have strong knowledge in PHP you can move to plugin development.

 

yes i have knowledge of php...but have not knowledge of designing.....

 

If you already have php knowledge, but no experience in designing, probably will be best for you to start designing WordPress plugins. This will require more php and programming skills.
First of all, you need to be familiar with WordPress and how things work: WordPress specific functions and WordPress way to do things.
You can learn most of this things from http://codex.wordpress.org/ .
The best way to learn is practice, so you'll always need to do new things (not only theory). Most of things you'll learn from mistakes and practicing.

Later, you can start edit themes and even start designing some from scratch. Anyway, to design both plugins and themes, beside PHP, you will need to have HTML knowledge and CSS, and some JavaScript basics (especially jQuery).