I will try and simplify to give an overview. If you think of preparing a Joomla site pretty much as you would prepare the publishing of a book. First you give the book a name and author, in Joomla this equates to the site name and administrator in the first instance, other authors can be added later. Then in a book you’d have a preface or introduction, in Joomla you might create some featured articles that appear in your front page. You’ll see in admin that there are two tabs articles and featured articles, thats the difference, the featured articles are those that remain on your front page and the articles are attached to categories. Categories are something like chapter headings, they contain the articles. In later versions of Joomla you can nest categories within each other.
Above all this information site the menu system which allows you to call on the information as an ordinary menu would; but allows you to define how you want to display the result – e.g. a blog or list etc.
Before your information is displayed on your website you have to publish it via a link in admin. One clever aspect of Joomla is that you can prepare an article in advance and show what date you want to pubish it and when to stop the article being available. This allows an author to prepare in advance and not worry about deadline material – show dates etc- to remain on your website as dead material.