The User Stats tab is a great way to see the overall progress of how your users are doing. The first box is the combined progress of all users and the proceeding boxes after are for individual users.
As for the box to the right:
When you click “New Leads Needing Action”, you will be directed to a list of new untouched leads.
When you click “All New Incoming Leads”, you will be directed to a list of emails that need to be replied to.
When you click “Recalculate Stats”, everyone's statuses will be refreshed.
The User Activity tab shows a list of all users and who is contacting their leads.