I learned about the OSI [Open Systems Interconnection] some years ago. It is a bit of a hypothetical model of how data flows from top to bottom, and from bottom to top. In other words, it explains and gives an overview of how data flows, starting for example, from the moment you type a keyboard character in Microsoft Outlook to the point at which the person reading your email opens the email.
The explanation is given by way of segmented stages of network communications, as seen in the image. A lot happens during this process! In reality, it can be very, very complicated to understand every single detail of each stage. But at least the “OSI Model” provides for a concrete beginning to understand it all. I was taught to remember it by way of this acronym [bottom to top]:
“Programmers Do Not Throw Sausage Pizza Away”.