A golf duffer’s guide to the portable handicap.

The former, system, in Great Britain and Ireland, is only one of six systems used around the world. The new system, developed jointly by the R&A and the USGA, is designed to make the game more accessible and to provide a handicap that is portable throughout the world, consistently reflecting a player’s true ability, providing a fairer basis for competition on any golf course anywhere. 
If you already have a handicap, your new Handicap Index will be calculated automatically, using the best 8 scores from your last 20 rounds. The maximum Handicap Index for both men and women is 54. If you have been playing close to your handicap, you should notice little change. If you have not and have been protected by the One-Shot rule, the new system may generate a higher handicap.
Handicap Indices will, in the first place, be automatically generated from the scoring information held about you online and/or held by the Club to which you belong. 
It is called a Handicap Index because it is a measure of your demonstrated ability calculated for a course of standard difficulty. The objectives are portability, universality and fairness. Your Handicap Index will be adjusted to produce a Course Handicap appropriate to the difficulty of the course you are playing on.
The new system will take account of your score for the round, the difficulty of the course you played and the playing conditions on the day.
As you know, the par for the course is the number of strokes that should be taken by the Scratch player for the round. This is set by the Club. But most of us are not Scratch players, and some courses are harder than others. A more sophisticated assessment is required. This produces a Course Rating and a Slope Rating for every set of tees at each course.
The Course Rating is carried out by the governing body for golf in each country, using a set of internationally agreed yardsticks to determine a numerical measure of difficulty for the Scratch golfer. The Course Rating is not the same as Par, because it is not a measure of strokes taken, as such, but the result of a detailed assessment of length, hazards and other factors, hole by hole, to one decimal place.
 The Slope Rating reflects the relative difficulty of a course for players who are not scratch golfers in comparison to scratch golfers. Golfers use the Slope Rating, a trademark of the United States Golf Association, to calculate handicap differentials. The rating falls between 55 and 155; the higher the number, the more challenging the course.
Your Course Handicap is determined by the Slope Rating. Each player's Handicap Index is adjusted for this difference.
After every competition, a Playing Conditions Calculation (previously known as the Competition Scratch Score - CSS) will determine if the course was easier or more difficult to play that day to decide your Adjusted Gross Score. (So many definitions!) This is used to produce your Scoring Differential. The average of your best 8 Scoring Differentials from your last 20 games produces your Handicap Index.
When you are playing in a competition, there is a further complication. (Bear with me, please.) To make it fairer for better golfers you will only get a percentage of your course handicap, for the competition only. Thankfully, this will be worked out by computer. No maths ability required. 
Phew! It's a lot to take in, isn't it? Fortunately, it's all worked out for you. All you have to do before starting to play in a competition, at any club, is to check your Handicap Index against the Course Handicap Table for the tees you will be playing from to find your Course Handicap for that round. The Course Handicap Table should be displayed in the Mens’ and Ladies’ Locker Rooms in your club, on the club notice board, in the Pro Shop, and in most cases, on your Club Website as well. (Make sure you know which tees you are playing from before finding your Course Handicap. And write your correct Course Handicap on your scorecard to avoid disqualification from the competition.) 
If you have a nightmare hole, don’t panic. For handicap purposes, there is still a maximum score per hole of net double bogey.
You must submit your score before the close of play on the day you played, as handicaps are revised on a daily basis. The computer will, as now, make adjustments for a maximum score for any hole. An adjustment may also be made if the Playing Conditions Calculation shows that the course played easier or more difficult than expected. Your Adjusted Gross Score will then be used to produce your Scoring Differential. If your Scoring Differential for your latest round is one of your best 8 in the last 20, it will replace the oldest of such scores and may result in an adjustment to your Handicap Index.
Happy Golfing!