Here are some basics for adding a Joomla article (web page).

1. Create a Category (the equivalent of a file folder)
2. Create an Article or webpage (the equivalent of a piece of paper in the folder)
3. Create a menu link to the article (Folks have to have something on the website to click on to get to your new webpage).
   The menu system in Joomla is an important part of how Joomla controls content.

Everything on the website that is not an Article is a Module. (See Extensions > Module Manager)

When it's time to apply Modules to pages, you use the menu system. Therefore, every page of the website needs to be in a menu.

For example,  when you create a new Module announcing a special event, you can tell that Module to only be on the home page through the menu system. Your logo, for example, is in a Module, that is being told to be on all menu links. If you open any Module, you will see a tab called Menu Assignement, here you will see all the menu links.