This is an adaption of an article by Jim Loy explaining parts of the acol system I use
I can't think of a good opening to this so I will just go straight into the bidding system. I will describe the bidding process in the order that I think for a bid. I will also explain why this bid might be used as best I can. I may give optional bidding methods and bidding examples.
To make things slightly easier for beginners I will quickly run over suit order, counting of points, finding a fit and stoppers.
The order of suits is alphabetical with the first suit starting at the bottom of the order.
Suit Order:
Majors:
Spades
Hearts
Minors:
Diamonds
Clubs
Points can be divided into 2 sections, high card points (HCP) and distributional points (distributional points should only be added to your HCP once you have founds a fit). You can not add DP to your HCP in a NT contract. Together DP and HCP are referred to as total points.
High Card Points:
A=4HCP
K=3HCP
Q=2HCP
J=1HCP
Distributional Points:
Void=3DP
Singleton=2DP
Doubleton=1DP
Game: is defined as 100 points
in rubber bridge. Contracts that reach 100 points include 3
NoTrumps (100), four of a major (H/S) (120) and five of a minor
(D/C) (100). In contract bridge reaching these contracts gives
you additional points on the score for that round. In both cases
reaching game is desirable. There are a generally accepted
number of TP required for game. As a general rule the minimum
number of TP for game in each different contract are
3NT=23+ HCP
4H/S=24+ TP
5C/D=27+ TP
Fit: is a working majority in the suit which you are in and is generally accepted to be at least 8 of the cards in that suit between the 2 partners (eg. 5 in north's hand and 3 in south's or 4,4).
Stoppers: A game in NT does not require a fit, however it is usually necessary to have stoppers in every suit. A stopper is a card which is most likely to win allowing you to change suits. Stoppers include the A, K with at least one other card, at least two low cards to the queen and if necessary you can consider 3 low cards to the jack a stopper.
Weak 1NT:
Opening 1NT shows 12-14 HCP and a balanced hand. Balanced is
defined as no more than one two card suit
(eg:4,3,3,3;4,4,3,2;5,3,3,2). This is called a limiting bid, it
clearly defines the hand to your partner. From this point on
your partner decides where to take bid. Some people like to bid
a strong 5 card suit in a 5,3,3,2 hand but this will detract
from the 1NT bid. I would suggest that people should avoid
bidding a five card suit from a 5,3,3,2 unless it is a strong
major NB: you should bid this first and foremost if you can,
this is a limiting bid and gives alot of information to your
partner. Invitational, Limiting.
1 of a suit:
To open 1 of a suit you require at least 12 points. If your hand
can't be described by a 1NT bid then bid your longest suit. In
the case of 2 suits the same length bid the lowest of the 2 four
card suits and the highest of the 2 four plus card suits. If you
have 3 four card suits then you need to arrange with your
partner if you bid the middle suit or the suit above the
singleton. Invitational.
2NT:
Opening 2NT shows 21-23 HCP and a balanced hand. Again this is a
limiting bid. Because any positive response shows enough points
for game point asking bids are not required. Any response is
game forcing. Card asking bids can be used to find a fit,
generally stayman is used. Strongly Invitational,
Limiting.
2 of a Suit:
An opening bid of two in a suit can be used in 2 different
ways. You will have to arrange with your partner which method
you use where. (strong/weak refers to the number of points in the
bid).
Weak 2's: Using weak twos a you should bid 2 of a suit if you don't have opening points (6-9 HCP) and have 6 of the suit. Invitational, Disruptive, Limiting.
Strong 2's: generally require 21+ HCP and at least a strong 5+ card suit otherwise bid NT. The points may very some you will have to agree with your partner as to how you define strong 2's if you use them. Invitational
Often weak 2's and strong 2's are used in combination. Most acol systems reserve 2C as a strong 2 indicating 23+ HCP and a good suit. The rest of the 2's bids are for weak 2's. with this system if you want a weak club bid then you have to use 3C.
2C: requires 23+ HCP. This is an unnatural bid in that it doesn't indicate a good club suit. The next bid by this person shows their suit.Forcing, Unnatural
Weak 2`s: As above.
3 of a suit:
Three level bids are reserved for pre-empts in most systems a
pre-empt is bid when you hold 7 cards and not enough points for
opening 1 bid. Point range for this bid is about 3-8 HCP
(open 1 at 9+ HCP).Limiting, Disruptive,Invitational.
4 of a suit:
To 1NT:
1NT has a limited number of possible response, these are:
Pass: if you have less than 6 points, pass. Likewise if you have less than 10 points and no good suit. Sign-off.
2 of a suit: is bid if you don't have enough points for game but have a long suit (at least 5 + cards) then you should bid 2 of your long suit. A response of 2 in the majors requires 6-9 points and in the minors 6-12 points.Sign-off.
Card Asking: There are a number of different methods used for card asking, the most popular is the Stayman convention. The Stayman conventions uses 2C to ask for any four card majors that partner has. This is the only forcing response, Partner must respond. If Partner has no 4 card major then they should bid 2D (artificial negative) otherwise Partner bids 2 of the lowest major that they have four of. If it was the suit that you required then you can proceed bidding as normal with a fit in the major.
Forcing.
Points Asking: you know your partner has 12-14 and so in general can work out if game is on, however there is a range in which you can be unsure about game. If you know a suit in which you have a fit then you can ask for game by bidding 3 of that suit. You should be game asking if you have:
10-12 TP in the majors
13-15 TP in the minors
no fit and 10-12 ask in NT by bidding 2NT.
Invitational.
Game: if you have enough cards and points to go to game, then you should. To go to game you should have at least 5 preferably 6 cards. If you only have 4 cards in the majors and enough points to go to game then you can card ask with the Stayman convention. If you don't find a fit using Stayman then go to game in NT. You should prefer NT over a game in the minors if you have a 4 card minor. If you find a fit then you should have at least 12 points for the majors and 15 points for the minors to go to game.Sign-off.
If you need to card ask and point ask then you should card ask first with the Stayman convention.
To 1 of a
Suit:
If you have a fit for your partners suit (4 cards in your
partners bid suit) and and more than 6+ points you should respond
with support in your partners suit. The level that you take the
bid depends on the points you hold and if the bid is in the
majors or minors.
Majors:
6-9 TP = 2 H/S
10-12 TP = 3 H/S
13+ TP = 4 H/S
Minors:
6-10 TP = 2 C/D
12-14 TP = 3 C/D
15+ TP = 5 C/D
All these bids are Invitational
If you don't have 4 card support and have 6+ HCP then you should bid your longest suit at level 1. You need 10+ HCP if you need to take your bid to 2 to bid your longest suit. You should maximize bidding space and bid the lowest you can from any set of suits the same length. forcing
To 2NT:
All responses to 2NT should be game forcing, however 2NT is
similar to 1NT in the responces that can be made. You should
respond with 5 points as you can make game.
Pass: if you have less than 5 points. Sign-off
Card Asking: If you have a four card major then you can use Stayman by bidding 3 clubs. If you have 5 cards in a suit then you should bid 3 in that suit and let partner choose it or NT. Game Forcing
Game: if you have 6 cards in a suit and biddable points then go straight to game in the suit. Otherwise with a balanced hand and points bid 3 NT Sign-off