Newcomers to Drupal who aren't tech savvy often struggle with the concept of Content types and Nodes.
I find it beneficial to remind them of the real world equivalent—forms and filling in forms.
Remember in the olden days when you were given a piece of paper out of a whole stack of them, with labels and boxes and you used a pen to fill in your information by hand (name, address, DOB, etc.) when applying for a college or anything?
The Drupal equivalent to a real-life stack of blank sheets of preformatted forms is a Content type. When you're creating a Content type in Drupal, you're actually designing a form of blank fields. You're designing a structure, it holds no data.
In the digital world, we don't have to have multiple copies of Content types, one is enough because it doesn't have to be printed on paper. It is printed on the screen and we can always use the same "source". That's way we only have one “Create article” form and not thousands of them like you have to in paper form.
When you fill in one sheet of paper in ink with your specific information it is considered one form submission. The Drupal equivalent to this one filled-in sheet of paper is a Node. Node is the actual data entered into the structure defined by the Content type. You can create many Nodes (data submissions) for a Content type.
When you want to publish an Article you are first presented with a form to fill—Create Article page. This is the Content type form. Once you enter specific data into it and Save, you have created one submission of that form, one Node. You can create many nodes, with different data, as submissions to the same form.