Help!, why does my new female cat HATES my male cat?

The cat probably just hates him because it's a different cat. Introducing cats is hard- WAY harder than I thought it would be when I brought home a kitten to my 2 yr old cat. Try separating them into different rooms maybe with a baby gate. This way the kitten will feel safe and they can get used to being in the same house. It might take a few weeks but don't give up.