The Withdrawal or pull out method prevents pregnancy by pulling the penis out of the vagina before ejaculation. In order to be effective at preventing pregnancy, the withdrawal method can require a lot of control and self-awareness to know when ejaculation is about to happen. On the other hand, it’s totally free and doesn’t require that you do anything in advance (other than have a self-awareness and dedication to using the method).
Lots of people think the withdrawal method is not very effective because they have been taught that pre-ejaculate (or pre-cum) contains sperm. While this can be true, it’s common for pre-ejaculate to contain no sperm at all or very little sperm. This is one of the reasons withdrawal is actually 80% effective with typical use.