After finishing Magento installation its time to look at how you want your store to look, what theme will it have , and will the same theme feature across all your stores if you have more then one ?  Our tutorial shows you how to duplicate the default theme and begin to modify it to give you greater flexibility on the look and feel of your new e-commerce store.

Magentos’ file structure is divided into two key locations , one containing the files which our end user will have access to such as css and JavaScript and one containing the block, containers and actual code that will build up any given page.  For the default installations these paths are as follows when magento was installed to the root of your site:

For the building blocks of page construction – app/design/frontend/default/default/
For the accessible browser assets – skins/frontend/default/default/

In the installation above you can see that the file structure represent the hierarchy of the design aspects, in this case app/design/frontend/instance/theme/

When building a site it is a good idea to have a separate name for your instance and your theme , for example you may decide to call your instance e-commerce, and your theme standard-blue.  Giving your structures and assets a strong naming convention will help you to organise and navigate your files with ease.

So the first stage to building a new theme is to copy the two above folders and rename them as you see fit.  This will give you two new sets of files to upload to your server via FTP.

Magento will now be able to access your new instance and theme and that means we can apply our new files as standard to our store.  To do so log into your Magento admin area and choose ‘System’, from the drop down menu choose ‘Configuration’.  Once the configuration screen loads choose the ‘Design’ option from the menu on the left hand side.  If you have followed our tutorial ‘Setup a new store’ you can choose the store you wish to configure the design for by selecting it form the drop down menu in the configuration scope.

Within the design configuration panel there are two key elements we want to change, the value next to the label ‘Current Package Name’, change this to your new instance name, for example e-commerce’.  The value next to the ‘Default’ label under the themes section needs to be changed to your theme name, for example ’standard-blue’.

With these changes made choose ‘Save Config’ to have magento start to use your new files.

src: http://www.magento-tutorial.com/