The "Storyline" Diary section presents the main plot of the game. Each new story page is unlocked as you unlock locations. A location's story is divided into 5 parts corresponding to 5 storyline collections.
You get a useful Talisman after completing 5 parts of the story (that is, assembling 5 storyline collections).
To jump to a storyline quest, tap the "Show" button on the Goals page.