The one convention that even beginner know.  The basics are:

1NT - 2♣ (Stayman) - 2♦ = No 4-card Major.

- 2♥ = 4-card Heart suit (may have 4-card Spade suit).

- 2♠ = 4-card Spade suit (denies a 4-card Heart suit).

Note: 

1. After 2♦  if responder bids two in a Major this shows a weak hand with both Majors.  The suit bid is the 5-card suit.

2. Stayman can be either 'Promissory' and responder must have one 4-card Major, or non-promissory.

There are several additions to the Basic Stayman.

Extended Stayman:

After the sequence 1NT - 2♣ (Stayman) - 2♦.  Bidding 3♦ asks for openers better 3-card Major.  Responder would be 5-5 in the Majors.

Stayman In Doubt:

After a 2♥/2♠ response to Stayman bidding 3♦ shows a 4333 shape and a Major suit fit; opener converts to the best fitting game.

Puppet Stayman:

Useful if the 1NT bid can contain a 5-card Major.

1NT - 2♣ (Puppet Stayman) - 2♦ = No 5-card Major.

 - 2♥/2♠ = 5-card suit.

After a 2♦ response it is useful to get opener to bid any 4-card Major trump fit so the Stayman bidder continues with:

- 2♥ = 4-card Spade suit (denies a 4-card Heart suit).

- 2♠ = 4-card Heart suit (denies a 4-card Spade suit).

- 2NT = no 4-card Major.

- 3♦ = two 4-card Majors.