In Link Groups section, from the left to the right, there are two panels:

1. Brightspace groups: a list of all the groups that have been created in the course is being displayed.

2. TimeEdit: the timetable of each activity is available.

In order to link a group(s):  

1. Select the event from the TimeEdit groups panel that you want to link
2. Click on the Tick box to select the Brightspace Group(s)
3. Click on the Link button, on the TimeEdit groups panel

As soon as the linkage is done, there will be a confirmation pop-up message

On the Brightspace groups panel, on the left side of the groups name:

1. The linkage symbol will appear, to indicate that the action above is completed, and
2. The group will appear also in the  TimeEdit groups

In order to unlink a group:  

1.    Click on the rightward arrow next to the activity's name on the TimeEdit groups panel to unfold the options.

As soon as the schedule reveals,

2.    Click on the "x" symbol next to groups name, to remove that certain group.
or

3.    Click on the Unlink all button, to remove all groups at once.

As soon as one of the above actions is done there will be a confirmation pop-up message.

Now you know how to link and/or unlink groups in the GroupTool!