It’s slightly different from the traditional drop/add period that most colleges have. At Yale, there is no preregistration before the term begins (with minor exceptions), so students can “shop” many classes before officially registering. So many “shop” 8-10 classes before picking the 4-5 in which to enroll. For the OP, Harvard is similar.
But as others have noted, classes go on as usual. At Harvard some large gen ed lectures may use the first class as an introduction instead of a standard lecture, but that’s not the case for all. So if one is shopping 8 courses, one has to keep up with the work until deciding which ones not to pursue.