language is what a big group (most likely a country or a dozen of cities) of people could speak. for example, filipino is a language since we all can speak it. cebuano also became a language because a lot (most of the people) could speak.
dialect is what a certain group of people speak. it also could be like a version derived from the actual main language. the rest of the way us Filipinos speak are dialects.
also, our main language is filipino not tagalog. I forgot why but theres a big difference.