If the curriculum has never taught about CSS comments up to this point then I agree, it should probably be made clear here. But you can always use the googles to search for “CSS comments”.
Don’t feel dumb. This is a learning site, so it should probably introduce a new concept with an example (assuming it hasn’t already). The only reason I told you to search instead of just giving you the answer is because that’s a valuable skill you need to develop if you want to be good at this stuff. I’ll let you in on a secret. Web development (and programming in general) is about 25% actual typing on a keyboard (and that may be an overestimate) and the rest is either thinking about how to do something or researching online.