With your Web Site created and already linked to an account name, you will need to define templates and layouts.

Template: here is where the code itself is written. Among other things, it determines how the information will appear on the screen, including where the placeholders will be shown. The templates are put together in the HTML Templates and Shelves Templates folders.
Layout: it's responsible for determining which elements will appear on a page. It is the one that sets the placeholders (elements like banners, collections and others), that will be displayed to the end user. In order to work, each layout must be linked to a single template. You can find the layouts of your Web Site organized by folders in the Sites and channels directory.