OSI is just a model, there’s not all that much to understand there. It’s simply a way to categorize network technologies using a common language.
For example, people sometimes refer to TCP as a "Layer 4" protocol even though (a) TCP predates the invention of Layer 4 and (b) TCP is a square peg that does not exactly fit into the round hole that is Layer 4.
Imagine how bad the rest of it was.