In a "transfer," responder transfers a major suit to a partner who opened with one no-trump.
A response of two diamonds transfers hearts to the opener—a response of two hearts transfers spades.
There are no point requirements for initiating a transfer.
The opener's rebid after a heart transfer is two hearts, and after a spade transfer, two spades. One of the two is required unless the opener can "super accept" the transfer with a bid of three in the suit.
The opener should "super accept" with four cards in the suit, seventeen points, and an absence of a 3-3-3-4 suit distribution.
The responder has these options for his second bid:
If the responder has eight or more HCP, a distribution that is not suitable for no-trump (contains a singleton or void), and six cards in his major suit, he may transfer by bidding four diamonds or hearts; the opener responds at game level with four hearts or four spades.