An enlarger is nothing more than a device that projects an image from a negative onto a sheet of photographic paper which is then developed for a finished positive image. Raising the head enlarges the image while lowering the head reduces the projected size. This a very basic process.
This is the model I have always used: An enlarger and a camera are equal and opposite devices. They are practically the exact inverse of each other.
Whereas, with a camera, light reflects off your subject, goes through the lens and is focused on the film, in an enlarger light comes from the negative, goes through the lens then lands on the photo paper.
You don't need to concern yourself with the intricate details of the math and the physics but, if you think about the general idea of it, you'll see that everything about the way an enlarger works is almost exactly backwards of the way a camera works.
I'm the kind of person who needs to form a picture inside my head to understand the way things work. This "inverse" model really helps me to "see" the process in my mind so I can solve problems and answer my own questions.
So, to put it in a humorous way, if you know how to use a camera you can just do everything backwards and you'll know how to use an enlarger!