This may be a stupid question. Does the common app ask for a list of extracurriculars or do you sort of weave those into your essay?
Not a stupid question at all.
They have a section for it where you can list up to 10 activities. However, this 10 includes employment, sports, clubs, etc. So if you have more than ten, make sure to prioritize the more important ones. Or if you want, you can submit one to one school depending on how you feel or your prospective major, because you can always change/update it even after submitting to a college.
My recommendation would be to look at some summaries/overviews – https://content.xap.com/media/11882/common_app_overview_for_website.pdf for instance – or better yet, check out the Common App itself if you want to know specific details.