Your question is not very specific, basically asking for a full tutorial on the subject. Fortunately there are already many such posts here and elsewhere on the net. The Search feature can help you find many, but i'll reference some here that may be enough.

The Bad, the Ugly, and the Good of autovivification
Explaining Autovivication
Autovivification trick

Maybe you could give those a glance and see if they answer your question, or at least help refine it to be more specific.

In reply to Re: Autovivification identification by Loops
in thread Autovivification identification by gaurav

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