It’s very basic, all stories have it. They can be broken into 3 basic parts.
Beginning: You initiation into the story. Where you come to know about the world of the protagonist. This is the part were the world of the protagonist should be thrown out of balance. It should take up about 25% of the story.
Middle: This is that part of the story where the protagonist chooses to step outside into a world unknown. The forces of Antagonism, too, reach their epitome in this part of the story. It takes about 50% of the story.
End: This is the part were the protagonist and the antagonist are face to face. They have the final conflict which leads to the defeat of one side and the conclusion of the story. It is the last 25% of the story.
A beginning, a middle and an end are the basic story convention, all stories must have it.