Retired Documentation: You are using the documentation for version 1.7.3 which was retired in 2013. Go here for the latest version documentation or check here for your available upgrades to ExpressionEngine 3.
Building on the Basics
Now that you've completed the Quick Start tutorial you have the foundational concepts for developing web sites with EE. The entire development process basically boils down to crafting a design in HTML/CSS, putting the HTML/CSS into Templates, publishing content into one or more Weblogs, and then integrating the EE Tags that display the Weblog content in your Templates.
Making the Web Site Pretty
The visual beauty of a website is up to the HTML, CSS, and graphics used. The beauty of EE is that it will not interfere with your carefully crafted design. Instead it will integrate neatly into your HTML.
In the Quick Start tutorial we used really basic HTML. We did this because the focus was on learning how EE works with HTML. Notice that you do not have to use the supplied Template sets. EE gives you an incredible amount of flexiblity in constructing HTML and using CSS and is designed to be very similiar to traditional HTML/CSS website development. If you have an existing web site you can import your site's HTML into EE. Most of the time this just means creating new Templates and Template Groups in EE to match your current directory structure.
Most of the time adding functionality to a site is as easy as finding the appropriate EE Module and integrating the Module's Tags into a Template. For example, if we wanted to let people comment on the articles we published in the Getting Started Tutorial site we just created we would add the EE Tags from the Comments Module into the "article" Template.
The Modules and Tags section of the User Guide has a complete list of Modules, the EE Tags available in each module, and the parameters and variables available to each EE Tag.
EE also has a growing Plugin Library. A plugin is like a small module. A plugin will have a Tag or small set of Tags that allow you to add specialized functionality to your site such as modifying the appearance of text, display RSS feeds, automate tasks, and many other useful things.