"This is good."
זה is masculine, and זו is feminine. Feminine nouns end in ה or ת, but there are exceptions. If a noun denotes a woman, it is feminine and if it denotes a man, it is masculine, like mother and father. Names of cities, countries, and languages are feminine no matter how they are spelled. Like in all languages, of course, you're just going to have to memorize the exceptions.