If you select the Group menu from menu bar, submenu will come up like <Figure 1>.
<Figure 1> Group menu at OPC Client Main menu bar
Add Group : Add a group at current server. (Bottom of the list)
Insert Group : Insert a group at current group. (Upper what you select)
Delete Group : Delete a group which you select.
Modify Group Properties : It is menu to modify a group properties, which you select.
Add Item : Add a new OPC item at group which you select.
Reference) If you don't select the group or item (In case of selecting the server), Group menu will be inactivated like <Figure 2>.
<Figure 2> Screen for inactivated Group menu by selecting the server
Relate items)