+- numbers in front of each number correspond to a current file;
+ number: indicates the code line added to the current file;
- number: indicates the code line deleted from the current file;

The number of lines of code added or deleted in the file.

Pay attention to the last line: 6 files changed, 33 insertions(+), 42 deletions(-).
6 files were changed, 33 lines were added and 42 lines were deleted, which adds up to the total number of lines changed in all the files above.

The +- numbers after each file can let people see at a glance the proportion of added and deleted code in the file.

If you run git diff --numstat, the first two numbers represent the added and deleted lines respectively: