https://www.youtube.com/watch?v=lkAyPfAqs_8&hd=1

This shows you how to create secure channels that you can let only specific people enter, without having everyone of a higher power being able to enter and bypass the protection.

Also, it demonstrates how to set up admin positions that can bypass and enter all channels including secure ones, IF you really want that ability.

It is all explained and demonstrated so you will learn how to make secure channels. This is more advanced than merely setting a join power requirement and being done with it.

Really useful to people who want guaranteed privacy, or need only high level admins to be able to bypass certain channel-based restrictions.