You can use the text function to put labels at x-y coordinates. Name-value pairs can be used to determine where to place the labels relative to the coordinates (e.g. left, right, centered, etc.).
text(x, y, ["my" "labels" "etc..."])
I'm not sure what you were trying to do with a, b, and c in the above code, or if you have a separate question about that.
You can also select a web site from the following list:
How to Get Best Site Performance
Select the China site (in Chinese or English) for best site performance. Other MathWorks country sites are not optimized for visits from your location.