Most of the time they are either male or female sometimes you will get ones that have flowers of both sexs a hermi. This is usually caused by bad lighting. MJ plant will show its sex with pree flowers before it actually goes into its flowering state. Females will have very clear to see white pistils and the males will have balls. Its very easy to tell them apart once you see it for the first time. And yes you want to pull your males otherwise you will get very seedy buds.