The purpose of course-level student learning assessment is to find where students are struggling and succeeding and to make adjustments on the basis of those findings. The "loop" indicates that this is a continuous process of identifying outcomes, assessing learning, using this learning to improve teaching, and then once again to identify outcomes.
Closing the loop is the part of assessment where you get to take action, where you get to be creative and innovate, and where you get to "manage student learning." Based on your findings of where students are struggling or succeeding, you can decide how to adjust your pedagogy. For example:
Maybe you find that students are having trouble applying a major theoretical concept, as evidenced in a rubric analysis of the final paper. Perhaps they need more practice with this type of thinking earlier on in the course, so you decide to assign small projects that ask them to tackle the concept bit by bit and apply it in multiple circumstances.
Maybe you find that students can discuss some frameworks better than others, as evidenced by scores in an item analysis of an exam. Perhaps you teach the two frameworks in different ways, and can apply some methods from the framework with better outcomes to the framework with weaker outcomes.
Maybe you find that students are having trouble interpreting graphs in their final exam. Perhaps a component of the course is coordination with the Dolciani Math Learning Center or set of online exercises at Sapling to provide a deeper, more intensive exploration of this skill.
Maybe you find that students are having difficulty finding appropriate sources for their research paper. Perhaps collaborating on a workshop with the Hunter College Libraries could greatly improve student leaning in this area.
Hunter's Center for Online Learning is a great place to start to explore innovative pedagogical practice.