Only shifts belonging to opportunities you have pinned. Nothing else.
That is deliberate. Most administrators care about a handful of opportunities day to day, and a dashboard listing every shift in the organization would be unreadable for exactly the people who need it most.
In the My opportunities & schedule section of your dashboard, which displays the shifts across all of your pinned opportunities in one place.
From your Opportunities page, on the web.
Your dashboard, including everything you have pinned, is also available in the mobile app. Pinning itself has to be done on the web, since it is not available in the app yet.
Because nothing is pinned yet. An empty section is not a sign that you have no shifts, only that you have not told the dashboard which opportunities you care about.
No. Pinning arranges your own dashboard. It does not change an opportunity's visibility, it does not affect what users see, and it does not alter who is approved or scheduled for anything.