Action, personalisation, connection layers etc. - What are they in Braze?

Hello everyone!

What do these different layers (connection, personalisation and action) of the Braze tech stack correspond to in terms of functions/features? And how do these layers interact with each other in different scenarios?

I know this last question (on the sequence of a message through the tech stack) is one of the questions in the study guide for the admin certificate and it caught me completely off guard. 

Been looking throughout the documentation and have pieced together what the other layers "are" but can't find definite answers about these 3 or how they all interact in common scenarios. Would appreciate any insight!