HELP ME IN ABAP HR

1,WHEN TO USE RP_PROVIDE_FROM_LAST AND WHEN TO USE

PROVIDE (WITH AN EXAMPLE)

2,HOW IS ABAP HR DIFFERENT FROM ABAP

3,NEED FUNCTIONAL KNOWLEDGE IN HR MODULE LIKE

PA,OM,RE,PY(SOME GOOD LINKS)

4, WHAT ARE THE OPPORTUNITIES FOR ABAP HR PROFESSIONAL

THANKS TO ALL.