This popular convention is used when the OPENER rebids 1NT or 2NT. Responder bids the new minor as an artificial way to ask about (or "check back" on) the majors.

Example Auctions: In each of these auctions, responder's second bid is new minor forcing. The responder is asking the opener about the majors (typically looking for 3-card support).
1.

OPENER	RESPONDER
1	1
1NT	2

2.

Opener	Responder
1	1
1NT	2

3.

Opener	Responder
1	1
2NT	3

New minor is used only by the responder and always as his second bid of the auction. It promises at least invitational (10-11) strength (after a 1NT rebid) and some doubt about what the final contract should be. In most cases, the responder will have 5 cards in his major and be trying to decide if the hand should be played in his suit or in notrump.

Examples for Responder to match the auctions above:

1. 1-1-1NT-2:
   K Q 10
   A Q J 7 3
   Q 3 2
   3 2
   
2. 1-1-1NT-2:
   A Q 10 8 5
   K J 7 5
   K 2
   5 4
   
3. 1-1-2NT-3:
   
   K J 8 5 4
   5
   Q 7 6
   7 6 5 2
   

In each hand above, the responder is hoping the opener can show 3-card support for his major. When the new minor is bid, the opener must ALERT. If the opponents ask, he can explain: "My partner's bid is artificial and forcing for one round. He is asking me about my majors." The opener now should show 3-card support if he has it (with 4-card support he would have raised on the previous round). If the opener doesn't have 3-card support, his next obligation is to show 4-cards in the other major. If he has neither of the above, he makes the cheapest bid he can (over clubs he bids diamonds; over diamonds he bids notrump).

Meanings for Opener:

Opener	Responder
1	1
1NT	2
??

2=3-card heart support
2=4 spades, but not 3-card heart support (unlikely since no 1 bid)
2=None of the above.

Opener	Responder
1	1
2NT	3
??

3=No major
3= 3-card heart support
3=4 spades (not 3 hearts)

*Note: If you play this convention, make sure partner is playing it the same way as you. I suggest you play it as written here, but some people play that on Opener's 3rd bid he bids his cheapest major (up-the-line). (In other words, he might show 4 hearts before showing 3-card spade support.)

Examples for Opener:

1. K Q 2
   J 4 3 2
   A Q 2
   Q 7 6

OPENER	RESPONDER
1	1
1NT	2
??

Bid 2 (unless you are playing that you show hearts first with 4 hearts and 3 spades)

2. A Q 3
K J
K Q 10 5 2
K 4 3

OPENER	RESPONDER
1	1
2NT	3
??

Bid 3 (Denying 3 and denying 4)

3.

AQ
AJ5
A10432
K103

Bid 3

Follow-ups (Responder's 3rd Bid):

Opener	Responder
1	1
1NT	2
2	??

A bid of 3NT is "Choice of games," promising 5 cards in his major.
A bid of 4 of the major is to play.
A re-raise is invitational.

Examples:

KJ954
AJ3
K54
J2

On the auction above, bid 3NT to offer opener a choice between 3NT and 4 (he will know you have 5 spades to have gone this route).

KJ954
3
KQ4
KJ72

On the auction above, bid 4 to play in the 5-3 fit (this hand is too shapely to offer opener a choice between 3NT and 4).

KJ954
3
KQ4
Q872

On the auction above, bid 3 to invite game in the 5-3 fit.

Note: "New Minor" should NOT be on in competition (of any kind). Decide if you wish to use it by a Passed Hand (No strong feelings--just make sure to discuss).

"New minor" can be used after 1-1-1NT (with 2 being the aritificial bid).

You might consider Larry's recorded webinar on New Minor Checkback found HERE.