To summarize this story in four sentences, you must be very succinct and mention only the essential details of the story. Essentially, David Sedaris is writing about his experiences learning French as an adult. Though he has studied the language before, there is much he doesn't understand, and he recounts his feelings of being shamed and embarrassed by his teacher. In the process, he bonds with his fellow students, as they are also facing the same feelings of shame. Eventually, he comes to understand what his teacher is saying, including the insults. In your summary, you have decide what is essential and what are details you can leave out.
As an example, I will provide a three-sentence summary. This is an example, as you should figure out on your own what is essential to include. Here is the partial summary:
David Sedaris writes about his experiences studying French as an adult in Paris. The teacher continually shames him and the other students. Sedaris feels a sense of terror; he spends many hours a day doing his homework and trying to use the language on the streets of Paris.
I'll let you think of what the final sentence should be here; it might include an explanation of the ending of the story or what Sedaris learns from his experiences.