Each Candidate can be assigned one group. You can create as many Groups as you like. There is nothing significant about a Group but it provides a way to view Candidates that all share a particular attribute. If a Candidate is assigned to a training class, then it may be beneficial to create a Group for that and assign Candidates to it. You should not create groups that represent a Candidate's status. POBITS already has attributes for that which you will find more useful.