Drupal is a content management system. So what is a content? Content is what the user sees. This page, which you are reading is content.
Creating and publishing content
First, you need to create your content and publish it. Then it will be visible to other users.
To create a content, go to Content > Add Content and select the content type you need to create (e.g. Basic Page).
Create content by filling all fields.
Before saving, check if the publish option is selected under Publishing options.