reforging isnt a profession.
its an npc in the enchanting vendor in dalaran. there was one in SW where the inscription guy was but i dont know about hordes location. most likely near the enchanting or inscription.
Mastery is on your gear. depending on what spec and class you are they are all different.
For example holy paladin, when you heal with a certain spell (not sure if its holy shock or light you place a bubble on the target absorbing X amount of damage. every point in mastery increases the amount by 1.25%/
For ret pallys it increases the damage done by crusader strike by 1.25% every point.
Dont quote me on the numbers or abilities, its been like 9 months since ive played cata =D