How do QA Activities fit in to Agile or Scrum processes?

My organization is starting an agile project based on the Agile v5 template. However we have questions about how QA activities are integrated into release and sprint planning. The template process guidance does not really address these issues. I would appreciate any information about how this is typically done or where I might find discussions or articles on this topic.

There are two major issues we have questions about:

1. How does release and sprint planning account for the fact that development and QA activity timelines do not start at the same time?
2. How are defects cycled thru release and sprint planning activities?

Thanks