Your site content management system resides at: www.yourdomain.com/administrator/
Once in the Control Panel you will be able to go anywhere in the site, whether clicking on any of the icons in the control panel, or selecting from the pull down menus of the Joomla main navigation. On the left side you have a list of every major area of the CMS: Articles Manager, Menu Manager, Extensions Manager, etc.
Joomla is very easy to use. There is a logic to it. Figure it out. Just pay attention to a the way the interface works. It is mostly the same throughout. When you are in a new area, you will have the same icons, but they pertain to the area that you are in. So, if you go from the article manager to the categories manager, you will have the same looking buttons, but they now pertain to the categories, not the articles, and so on.
The J3 top Navbar and its dropdown menus allow you to easily navigate throughout you site. I have added screen shots of these menus to help you familiarize yourself with them.
Navigating the Joomla 3 CMS
There are a few things in this area that you might need to know about... The main metadata (SEO) for the site is inside the Global Configurations. The Clear Cache is a good one to remember. If you ever have any trouble with the site, that is the first place to visit. Clear the cache and see if that relieves the problems.
This is where you manage your users. You can add users to your site, block users, or change the permissions that user can have in the site. (What they can and cannot access).
This is where you create or manage your menus (site navigation).
Your site's content: articles. categories and media are in this area. Your site is made up of articles, categories and media. Your articles are the main content in your pages. The Article Manager contains all your articles. You can group articles into categories to better organize them, but also to create blogs, or lists. You can create a category and then assign this category to the articles you want to include in a blog or list. All your graphics, photos, documents, and PDFs are kept in the media manager. Featured articles are a little more advanced. You can define an article as featured and then display all featured menus on the fly.
Components are software that extend Joomla. It brings several already installed, but there are many options out there for all your needs: Extensive form makers, real estate programs, slideshows, event managers, and much more.
Extensions are little apps that allow you to add different kinds of content to your site. Modules must live in a module position in your site. Plugins can either work behind the scenes or must be called to action by inserting a little bit of code in your articles.
Probably the most important menu of all. You can access help about the manager you are in from anywhere in the CMS. If you are in the article manager and you need help, click on the help button. This will bring up an article about how to work with the article manager. There are many additional resources. Also, there are many great forums out there and I have found the Joomla community to be very helpful and friendly.