The Back End Main Page
When you first log into Joomla's backend, you'll come up to the backend main page - also called the Control Panel - which is basically a jump off point for all the basic functions of Joomla.
On the right side, there's a welcome page of sorts that also hosts some fairly useful information, such as what users are currently logged in, as well as what articles have done well, and even the statistics for your menus.
Here you can see that you have a button-style menu at the left of your screen which includes several of the most commonly used functions in Joomla. Here are some basic explanations of what function each button handles.
Add New Article: This allows you to add a new article with a click of this button. Frequently used by bloggers and websites that are just starting up, having this conveniently located at the very front will make updating a breeze.
Article Manager: Joomla allows you to shuffle articles from section to section, archive, unarchive, remove from the front page, and edit and update old content from the article manager. This is highly useful for those of you (like me) who are constantly updating and shuffling around their work as new articles happen.
Front Page Manager: This is intended on helping you make managing your front page a little easier. Basically, the functions within this section will help you control what articles you display on the front page, in what order they are displayed, and allow for quick-editing of any of the front page articles.
Category & Section Managers: Furthering the organization you get with Joomla, you can place your articles within a category, and categories within a section. For example, you can place individual blog articles within a category called "March 2010" and individual categories such as "March 2010" and "April 2010" within a section called "Blogs." For more information on Sections and Categories, check out the Sections Vs. Categories tutorial.
Media Manager: Managing the media on your website - which includes mostly images, but can include video and audio as well - is as simple as uploading into the media manager. This is convenient for uploading a file quickly into Joomla. However the downside to the media manager is that you can only upload a single file at a time, and your files must be smaller than 10MB at any given time - this can, however, be sidestepped by using an FTP client instead of the media manager.
Language Manager: The language manager provides a quick and easy place to change the default language for both your Joomla front end and back end of your site. Additional language packs have to be installed after your initial setup.
User Manager: By accessing the user manager, you can easily add and delete users, see who is currently online, log off users, send messages to individuals or groups of users, and change the individual permissions of each user.
Global Configuration: The global Configuration allows you to change the configuration of your Joomla website. This includes your META description and META keywords, site name, your default WYSIWYG editor in Joomla, and a few other options. It is here that you can also set your site as "offline" while you go through the process of updating.