Receivables Credit Note (transaction type RC) is found in the Finance/Receivables tab, and is used to provide a credit to a customer, by passing a corresponding debit in a GL account code. There are no products or services to select in this transaction, and there are no inventory impact using a RC transaction.
Goods Return Credit Note (transaction type CC) is found in Sales/Operations/ Goods Return Credit Note - and is used to provide a credit to customer who bought products and services from you. User select strictly products or services to perform a return, and there is no access to the GL account codes. For stock items entered in this CC transaction, the inventory will be added back into stock when posted.