Translation:It's a cat.
If you want to say you are something, than you often just say: (word) desu. Cause everyone knows what you mean, but if you want to say something specific or unusual senteces like: I am a cat. You would say: Watashi wa neko desu / 私は猫です. So everyone knows that you want to tell that YOU are the cat.
Is it too much to ask that Duolingo recognize the kanji for cat (or any other word they are teaching us)? Sometimes it accepts 猫です and sometimes it marks it wrong, saying the correct answer is ねこです.
There is also no option for "my answer should be accepted" under the report button, which is why I'm commenting here instead.