Ctrl-G : Add selected objects to group?

In Help`s Hotkey MouseAction Reference at the letter G it says:
Ctrl-G : Add selected objects to group
Shift-Alt-G : Remove selected objects from group

I thought that groups exist only by parenting few objects to some other object. Is there a way of creating groups without using parent??? Because Ive tried these shortcuts and they dont work. Or maybe Im doing something wrong. But if they really dont work why there are those shortcuts in the help Hotkey Reference?