Sure, let's break it down:

1. import sys: This line imports the sys module, which provides access to some variables used or maintained by the Python interpreter and to functions that interact strongly with the interpreter. It is a standard Python module.

2. import matplotlib: This imports the matplotlib library, which is a plotting library used for 2D graphics in python with applications in many different fields.

3. matplotlib.use('Agg'): This sets the Matplotlib backend to Agg (which stands for Anti-Grain Geometry). It's a high-performance library for rendering vector graphics, and is used by Matplotlib to create plots.

4. import matplotlib.pyplot as plt: Here, matplotlib.pyplot is imported as plt. Pyplot provides a convenient interface to the matplotlib object-oriented plotting library. It's modeled closely after Matlab, thus the name pyplot.

5. x = [5,7,8,7,2,17,2,9,4,11,12,9,6] and y = [99,86,87,88,111,86,103,87,94,78,77,85,86]: These lines generate two lists, x and y, that will be used as coordinates for scatter plot points.

6. plt.scatter(x, y): This calls the scatter method of plt to create a scatter plot of x and y.

7. plt.show(): This displays the plotted graphic. As the backend is set to Agg, this command might be ignored.

8. plt.savefig(sys.stdout.buffer): This saves the final figure to the buffer available at 'sys.stdout.buffer'. It won't create a graphic file but you will be able to get the byte representation of the image created.

9. sys.stdout.flush(): This command forces the system to "flush" the output buffer, meaning that it will clear anything that's in the buffer.

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