In order to read a greens slope, you will need to first understand what the numbers on a golf course rating chart represent. The numbers on the chart range from -2.0 to +2.0, with the majority of courses falling somewhere in between these two extremes. A course that is rated as a -2.0 is considered to be very easy, while a course rated at +2.0 is extremely difficult. Most amateur golfers will have a tough time playing anything above a 0.0 rating.
The next thing you need to know in order to read greens slopes is how to properly interpret the contour lines that are typically found on golf course maps. These lines indicate changes in elevation, with the closer together the lines are, the steeper the change in elevation will be. For example, if you see two contour lines that are close together, this indicates that there is a large hill or mound present. If the contour lines are far apart from each other, then this usually indicates a gradual incline or decline in elevation.
Now that you know how to interpret the numbers and contour lines on a golf course rating chart, you can finally start trying to read greens slopes! When looking at a green from afar, take note of where the hole is located in relation to any hills or mounds present on the green. This will give you an idea of which way the ball will break when it hits these obstacles (i.e., whether it will roll left or right).
Once you have determined where all of the obstacles are located on a particular green, it's time to start reading putts! To do this, stand directly behind your ball and look towards the hole (you may want someone else to act as your caddy so that they can help point out specific landmarks). From this vantage point, try to visualize where your ball needs to travel in order for it drop into the cup; this imaginary line is known as your target line.
Now that you have identified your target line, take another look at all of those pesky hills and mounds present on the green; specifically pay attention to how they might affect your target line (i.e., make sure that your ball doesn't get caught up in any divots!). If everything looks good and there aren't any obvious hazards present, go ahead and take your shot! Just remember: always err on the side of caution when reading greens slopes... after all