Im currently studyng creating wordpress theme from scratch and manage to create my own.. can anyone help me.
You cannot build or use your own custom theme built from scratch at ordPress.com. We cannot edit themes or templates here at all. http://en.support.wordpress.com/themes/editing-themes/ We have no FTP acces to free hosted wordpress.com blogs and cannot add themes. W are limited to the themes found in the dashboard under Appearance > Themes.
There are two free themes, Sandbox and Toolbox designed to allow maximum flexibility for CSS editing and creating new “skins”. Toolbox is more modern and includes a lot of support for CSS3 and HTML5, so it is really only limited by your skills and knowledge.
If you have CSS editing experience and purchase the CSS upgrade it will allow you to stylize the appearance of themes you find here > Appearance > Themes, but will not allow you to change the functionality, by editing the underlying template. It does not allow you to remove footer links to the theme designer or to WordPress.com. Also note that CSS is theme specific, so you cannot use the CSS stylesheets from other themes with the themes at wordpress.COM.
There is no official Staff support for the CSS upgrade, and precious little Volunteer support so do not purchase the upgrade unless you have CSS editing skills. If you do and choose to purchase the CSS upgrade read this before you begin editing http://en.support.wordpress.com/custom-css/#css-help
If that's not your choice then do note that by hiring a web host and setting up your own self-hosted wordpress.ORG install you can have total control over your template and themes. http://support.wordpress.com/com-vs-org/