Workflow

Workflow permissions can be set in this section, controlling which groups can move a defect from one state to another in Defect Tracking. A new defect that is filed starts off in the New state and depending on the groups allowed to make assignments, it is moved into the Assigned state. These groups are added by clicking on the '?' button on the arrow connecting the two states. In the Workflow Permissions window that opens, Group(s) and Assigned Group(s) are listed and groups can be moved from one list to another.

By removing all groups from the Assigned Group(s) section of the pop-up, that state change cannot be done.
The QA group is assigned to all state changes by default.
This workflow cannot be altered nor can you currently customize the state names.
Defects must be moved from one state to another as per the directional arrows (e.g. you cannot move a defect from the New state to Verified directly).
If you have not selected groups for a particular transition (that is, the Assigned Group(s) section is blank), that transition is effectively not allowed.