I agree with both of you, lyrehc and smiley on this. I agree with Smiley that kisses don't necessarily have to lead to sex. But there is a progression, and if people are not aware of what is happening, they can end up having sex before they know what they are doing.
Okay, so first, in the animal world many of the males are the beautiful creatures to attract the female. It seems to work the opposite with us humans. The young many who is hoping to attract a mate will dress and groom as best he can including the nice smells and the works. The young lady is the one who usually goes for more beautification including all the colors of the rainbow, and I love colors!
All of these qualities help with attraction. The male is naturally attracted to the female, and he really wants to have sex with her. I understand that the female also wants to have sex with the male, but from what I understand there are other things that are important to her that the male is not considering, or at least doesn't consider important.
So as a couple you love the way each other looks and smells. You love the way each other talks, and you are naturally attracted to each other. So you have desires for each other. You love each other's company, and so at this point caution is important, because one thing leads to the next. You take her hand so innocently. You give her a kiss on the cheek. You are so taken with her that soon you are kissing her on the lips, and a little voice says, "Go ahead proceed; it feels so good and it is right! We have all heard the expression "take it to the next level," and that is what you are doing. Before long you are pressing your body against hers, and hers against yours. You are touching her skin, and before long your hands are going where they shouldn't be going, but it all feels so good, and so right. You are soon massaging each other, running fingers through hair. You hormones are running high, and before long you are pulling each other's clothes off, and then the end comes when you actually do have sexual intercourse. After marriage this is all fine and wonderful, but before marriage it can come back around to sting you in more than one way. This is true for what we call pre marraige sex or fornication, or extramarrital sex or adultery, and it is sin, but God forgives, so don't beat yourself up if you have gone down this road, just ask God for forgiveness, repent, and live differently.
So kisses can lead to having sex, but not necessarily so. It all depends on where you stop this process, or progress before the sexual act is started. Don't take it too far because remember it is a very strong drive, and once you start it, you may not be able to stop it until it is finished!