Issues are routed according to issue state and state owner. A state owner is a role in your organization that is responsible for an issue in a given state. For example, in the default workflow, QA has responsibility for issues in the Unreviewed state.
Now you must assign an owner to each state in your final diagram. Finally, decide which groups should have permission to take each action. In the default workflow, for example, only users in Development are allowed to fix issues (that means, take the Fixed action).