-u option you used specifies the unified format. In that format the first two lines is a header:
--- is the original file,
+++ is the new file, and the timestamps.
@@ block headers
That is then followed by chunks (change hunks) that starts with the
@@ -R,r +R,r @@ syntax.
Those are two ranges, the one with the
- is the range for the chunk in the original file, and the one with the
+ the range in the new file. The
R designates the line number where the diff operation is started.
The numbers after the comma are the number of affected lines in each file.
- Every time you remove a line, the
+rnumber will be smaller than
- Every time you add a line, the
+rnumber will be bigger than
- Changing a line will add
+rnumber. (same scope of lines)
Chunks of code lines
Within these chunks lines are identified as additions or deletions
- means delete,
+ means addition. Lines that did not change in that chunk will have neither
- front of it.
In your example it means there are two chunks, or sections, that changed between the two files and the lines with
+ in it are the new ones added, nothing was deleted.
You can find much more information about the syntax by doing a google search for unified diff.