What Is WordPress
WordPress is the most used CMS (Content Management System) in the world.
How To Use WordPress
The Administration Panels serve as an intuitive backend for site managers. You will mainly be using the Dashboard to manage comments and view WordPress news, and the Pages and Posts tabs to create and manage content.
I suggest reading http://codex.wordpress.org/WordPress_Features for an overview of WordPress’ capabilities, then http://codex.wordpress.org/Getting_Started_with_WordPress for an quick overview of how to manage your WordPress site.