Intrinsic load is the natural load required to complete a task. It can be easy sometimes (driving from home to school) or heavy on others (being an air traffic controller), but we can be trained to cope with it.
The Germane level of load is the optimum level we can cope with, where we maximise the load we are under. In lessons and projects we can feel that Germane load as 'flow', where everything's going in our favour, and then...
Extraneous load comes along, where we all go wrong, especially when we are communicating information in, say, a presentation. It's when, mid flow, the grass starts getting cut outside. Or when someone has to leave a meeting early.
Overload occurs here. The person who missed the earlier part of the meeting, or left early, or the sensation that someone is talking at you when you're in deep conversation with another person opposite, or the kid who doesn't understand where you're at, who isn't with you because they didn't understand the initial point of the project...