You can start working on a task by right-clicking the project and selecting 'Team | Work On Task'. This will launch the Task Selection Dialog as described in the section called “Tasks”. From here can select a task which is assigned to you or assigned to a group you belong to (team). You can also create a new task to start working on.
You can associate tasks with the changeset in the Changeset Dialog as described in the section called “Tasks”. This allows you to associate multiple tasks with the same changeset.