Query on the concept of front end and back end in erecruiting

Hello experts!

We have SAP HR and SAP EREC in two different boxes( standalone I2b scenario).

Internal/external/recruiter/recruitmentadmin all are going to access erecruiting via portal.

Am I required to do any settings for switches BL2UI and UI2BL. Am also confused what is being called as front end and back end in sap erecruiting.

I have read a lot of blogs however unable to get hold of the concept.

Appreciate your responses!!

Thanks,

Poonam