RAC is reservation against cancellation
means you are not allotted any seats still you can go by the train
Normal situations RAC will become confirmed RAC if your name is put on list of passenger in the last hour
RAC people are allotted seats as per the asc. order of number by TTR on board train.
WL is waiting list a state before RAC.
If you are in WL list then you will come to RAC list then seat allotment.
please refer site