Answer:
The best way to tell what gender a cat is, it by looking underneath the base of its tail. A male cat that has not been neutered will have two furry testicles right below the anus, and a penis right below the testicles. A neutered male cat will not have visible testicles, but there will be a noticeable space between its anus and penis.
Spayed and intact female cats alike will have a genital opening (vulva) which is a tear-drop shape located right below the anus.