Just click on Upcoming Deadlines in the Required Actions panel! If any users have either missed a course deadline, or have one coming up within the next two weeks in a course they've not completed, the name of the course, as well as the number of users, will be shown. Just click on the name of the course.
Clicking on the Details button will take you to the course progress page for that user.
If you want to send them a message, the Message All Users will automatically select every user in the list to be a recipient of the message you send. If you wish to only message select individuals, you can use the drop-down menu to select which learners you want to notify.
Simply fill in the Subject and Message, hit Send, and your users will receive your message in their inbox.