Since I don't know the story, I can't tell you the main plot. But generally, in such folk stories, there could be characters with different personalities who go through some sort of adventure or encounter some conflict.
I don't have knowledge of this particular story. But thinking about typical folk tales, the main plot might involve the two characters, Si Langgam and Si Tipaklong, having their own goals or desires. There could be a problem that they need to solve together or separately. For example, they might live in a certain place where a disaster is about to happen and they have to use their unique abilities (if they have any in the story) to prevent it. Or it could be about a competition between them to win the favor of someone or something in their fictional world.