Views on your stories are recorded when:
An impression is generated for auto-play templates.
In this case, 1 view = 1 impression, as your stories start to play as the page on your e-commerce store starts loading.A user clicks on one of your stories for click-to-play templates. In this case, 1 view = 1 click, for each of your stories.
In both cases 1 view is then also recorded for each tab viewed (each time a user taps to view the next tab). Note that views are stored on a 7-day attribution window: if the same user views a story or tab multiple times within 7 days, the view is counted only once. Only 7 days after the first story view is the user considered a new user and additional views are recorded again.