The page indicator represents the currently active page and total pages of an overlay that lets you navigate horizontally between content.

Principles
Stack are a container component, so they share design principles with cards and lists:
Clear Feedback: Pagers communicate where the user is within a carousel of content.
Contextual: The primary purpose of a pager is to provide clear and immediate context for the content it's associated with.
Concise: Pagers are small and precise in visual language.
Usage & Placement
Pagers show the user their current position within a linear sequence of content.
They are placed above the system bar area and under the content area.
Do
Don't
Anatomy
A pager is composed of a row of indication dots in active and inactive states.
A. Active (Current page)
B. Inactive page

When five or more dots are present, the additional dots are indicated with a smaller first dot and slide the entire row until the end is reached.
Customization
Pagers have built-in scrim, paging, and animations that can't be customized. Rather the content within the stacks pager is customized.