Your goal in Conception is to put the charms on some pure, innocent girls, raise their affection for you, then make babies with them. You then take these babies out to dungeons for what appear to be turn-based battles.
The "star children" aren't made the way you and I would make a baby. Itsuki and one of the twelve heroines pour their spirit into some sort of device, and the baby is born after growing a bit.
The child's type is determined based off the parents. You can end up with a mage, a warrior, a monk, and so forth (yes, this is an RPG). Also, the child will end up with parameter boosts depending on the circumstances.