This feature can be used by the author(s) to link a group to an exam so that all the candidates present in that group can take the assigned exam. To use this feature click on "Assign Exam to Group" option in main Author menu.
A new window will open which will list all the exams present in a drop down list and all the groups.
Select the Exam you want to assign from the drop down and click on check boxes provided next to each group to include (checked) / Exclude (Unchecked) the group.