You need to set the Main Tank and Main Assist for the Tank, so the Shaman will begin to do more. Depending on what you are doing, you may want to set the Shaman to Chase to follow the tank as you explore or Assist to stay at a camp and bring mobs with your tank back to where the Shaman is.
You're new, so no problem, but the forums have dedicated sections for topics and resources. The CWTN (ChatWithThisName) plugins each have thir own section in the forums for question for that specific plugin. Please post in the MQ2Shaman discussion for more questions. Questions are good, don't hesitate, but also please read the FAQ on the page of MQ2Shaman, will save you time.