====== I assigned my co-worker for a task. How do I know what is happening with it? ======

Every user has his own list of his open Activities on Home page. Activity is shown on Home page under My Upcoming and Pending Activity according to Due Date and it can be seen until its status is not closed. It is not possible to overlook any of the Activities.    

More details about event or task can be seen on the "All" view of Activity. Click the //More...// button to see a complete view. You can see status of Activity (Event's status: planned, held, not held; task's status: In Progress, Completed, Pending Input, Deferred, Planned). 

There is also another way to see some Activities. All documents in Produs IT are interlaced. If an Activity refers to an Account or Opportunity etc., it can be found on a list of this Account or opportunity etc.