Let’s start with the natural and the most likely seed you have probably saved in a jiffy bag somewhere as I once did. When it comes to natural standard seeds that come from both gender parents, there is no knowing what you will actually get. It is about 66% chance that your seed will turn to a female plant and the other 34% are gonna be male plants which is not that bad. It is difficult to tell what you got before the pre-flowering stages around the 4th or 6th week of the vegetative period unless you have wished so hard that it turns female, that it actually does :D. Best would be to wait to about the 2nd week of the flowering stage, when it is quite easy to tell.
If you are looking to breed your own cannabis strains and make your own seeds then this is your best option. If you just want to produce nice bud to smoke then feminized cannabis seeds would be a better choice.
To get set the plant to flowering stage you need to reduce the light that you are giving it to 12H a day.
Feminized Cannabis Seeds
As you have guessed it already, these type of seeds are genetically modified to remove the male chromosomes of the plant’s DNA. Damn that was scientific… what I am saying