Tutorial or instruction on global group?

I built a behaveour for my game, and I need that one function of this behaveour create an object, but I can’t create other than the object who have the behaveour.
I tried to use global group, but everytime I make a global group, it disappear when I change page.

Are there some page of instruction or tutorial on how to use group and/or global group?

As far as I can tell, the “global groups” feature has no use.