To play bridge, you must agree a bidding system with your partner.
The most common bidding system in the U.K. is 'Acol' 
Bidding systems use a coded language to show as accurately as possible the shape and strength of your hand. 
During the auction, there are only fifteen words available to describe literally millions of hands.
(Numbers 1 - 7, clubs, diamonds, hearts, spades, notrumps, pass, double , re-double.)  

Most bids have a 'natural' meaning. e.g. 1© = 12+ pts and at least four hearts.   

Over the years experts have developed bids whose meanings stray from their natural meaning. 

These bids are called conventional bids, and are agreed with your partner to have a different meaning
than would be expected.  Listed below are some of the first conventional bids that you will use.
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OPENING BIDS of  2§ 

When you pick up a VERY strong hand of 23+ pts. (or game in your own hand) open with 2§
Responder will bid 2¨ with 0-7 pts.  Any other bid shows 8+ and slam can be investigated.
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OPENING BIDS of  2¨, 2©, and 2ª

When you pick up a strong hand with 8 playing tricks and at least 2 defensive tricks outside your trump suit you can open the bidding at the 2 level. This opening bid cannot be passed by partner

Responder will bid 2NT, with 0-7 pts.  Any other bid shows 8+ and game will be bid.
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STAYMAN

A 2§ response to a 1NT opener, or 2NT opener is a question. Do you have a 4 card major? 
Opener rebids :
2¨ with neither,       2© with 4 hearts, or with 4 hearts AND 4 spades,         2ª with 4 spades. 

The probe is usually to find the right game, but it can be made with an invitational-strength hand (11/12.)
If opener rebids 2¨, showing no four card major, responder will either invite game by bidding 2NT or, with 13+, bid game in 3NT
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BIDS of  4NT (BLACKWOOD)

Before bidding to Slams it is wise to find out how many aces you have.
3NT is game, so a bid of 4NT cannot be natural.  It is used to ask partner how many aces they hold.
In response, partner will bid 5C to show 0 aces, 5D to show 1 ace, 5H to show 2 aces or 4S to show 3.

IF all aces are held then 5NT would be asking for kings on the same scale.