I have to write a sentence with a polysyndenton sentence structure; is this an example of one?

ex: I was stressed because the teacher inundated me with many projects and homework and classwork and materials

Yes.

http://grammar.about.com/od/pq/g/polysyndterm.htm

okay, how do I know where to put commas?

A polysyndeton sentence doesn't usually have commas.

Yes, the sentence you provided is indeed an example of using polysyndeton in sentence structure. Polysyndeton is a literary device where conjunctions (such as "and," "but," or "or") are used repeatedly in quick succession to achieve an artistic effect. In your sentence, the word "and" is repeated multiple times, connecting various items in a series (projects, homework, classwork, and materials). This repetition creates a sense of accumulation and emphasizes the multitude of tasks being described.