"Effeminate" is an adjective that means "like a woman". But it's usually used to describe men. A man who looks or acts somewhat like a woman can be called "effeminate".
This is different from someone born as a man who dresses like a woman, however. There are many terms for such people, including "transsexual" and "crossdresser".
If you want to describe a woman who looks like a woman, you can say that she is "feminine" or "girly".