Laughably is the adverb from laughable, and it works in one main way that students often miss: it goes in front of another adjective to say "so much so that it is a joke". Laughably small, laughably easy, laughably cheap, laughably bad. The meaning is not that the thing made you laugh; it is that the amount or degree is so extreme it cannot be taken seriously. "A laughably small salary" means the salary is insultingly low. "A laughably easy exam" means the exam was so easy it did not count as a test. This makes laughably useful — it is a compact way to criticise a quantity. Less often you will see it with a verb or standing on its own meaning "in a way that invites mockery", but the adjective-strengthening use is what you will meet most. Like laughable, it is critical, and it belongs more to writing and to sharp commentary than to gentle conversation.