Action board is a one stop solution which gives you a focussed view on all your open action items at a single place. Action board has 2 tabs: 1. For You: this will list down all the action items assigned to you by others. 2. By You: this will list down all the action items that you have assigned to others.
One can easily create an action item by just mentioning someone in comment and checking the assign box. This will create an action item for that person.
One can easily close an action item by checking on the task from the task list. This can also be achieved by checking on the task from the activity feed in the details page.