That's not correct English. "I ain't" is colloquial (not formal English) and means "I haven't" or "I am not". Colloquially you can say "I don't know nothing", meaning "I don't know anything" or "I know nothing" --- purists would consider this to be incorrect English as it is a "double negative" (or alternatively purists may interpret "I don't know nothing" as meaning "It is not correct to say that I know nothing, and therefore it is correct to say that I do know something"), but as a matter of colloquial usage, you will hear native speakers say "I don't know nothing" meaning "I don't know anything", in informal contexts. Colloquially, you can say "I ain't heard nothing", meaning "I haven't heard anything". Again, this is a "double negative", so purists would regard this as incorrect (or as meaning the opposite thing). If you are a non-native speaker then I would advise you not to use these forms of English but it is good to be able to understand them.