Understanding 1NT Forcing (Bergen)

Regardless of your system, 1NT is the likely response to an opening bid in a major. You can acquire the judgment needed to make the right rebids, raises and responses. 1- Which hands should respond 1NT, and which hands should not 2- "6-4 bid more." But should opener rebid the 6, or show the 4? 3- "It's NOT Impossible." Responder's Impossible 2 Rebid. 4- When responder is a passed hand, what's different? 5- How to cope with an opponent's overcall.