CRM Front End and Back End server group roles

Hi

I am working on a new CRM 2013 deployment where the Front End server group role is split from the Back End server group role.

Could anyone explain how these servers work together? Which one is aware of which one? How does the Front End server know to send jobs for processing to Back End? or Is the Back End knowing where to get the jobs form without Front End worrying about how and where to send the jobs?