Buddy, how do you think your mom and pop made you? Do you think one day he tripped while taking his pants off and fell on your mom who was lying down to do some leg lift exercises in the nude?
There's a lot of complex things in courtships, but usually, you have to talk a little bit about sex before it happens. In fact, hinting at it, bringing it up, being playful yet mature about it will make it more likely to happen.