Qualified crew members are those who have shown they are experienced and competent enough to perform their job well without the need for coaching and support. It comes approximately 6 months after your initial probationary period ends, provided you can show you meet the standard.
World Class Crew is the next level up, and these are crew members who are trained to operate as the CSM when required by the operation during disruption. There is one on each longhaul flight (2 on a 380) and they’re the acting SCCM in case the original CSM cannot operate.
Each level comes with an increase to the basic pay level. Qualified is a fairly nominal uplift, WCC is more significant.