Piazza is a message board where you can ask and answer questions about the WeBWorK, supplemental problems, and any other aspect of the course. Using Piazza is not required, but you are encouraged to take advantage of it.
There is just one section of MATH 100, meaning I am the only instructor that will be answering questions. Therefore, you should be proactive in not only asking questions on Piazza, but also answering them. Writing out a careful solution to a problem posed by one of your classmates is an excellent way to master the material.