To add users into your Groups: 

1. Click Users in the main top menu 
   
   
2. Click on the ‘Groups’ tab, select a group from the left side bar.
   
   
3. Click the ‘Add User to group’ button in the group details area.
   
   
   
   
4. Select a user to add from the drop down list, and the user will be added to the group. 

Easy!