The Breadcrumbs UI is quick view of an element's location in the page hierarchy. It is similar to the page structure panel (which displays the same hierarchy in a "tree" layout.)

You'll find the Breadcrumbs UI at the bottom left of the window.
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Any time you select an element on the stage, the breadcrumbs UI will indicate the hierarchy associated with that element, and display it from left-to-right.

For example:

In this case, the selected element is a text element, which is inside a container, which is itself inside of a grid element. 

You can click on any element in the hierarchy to select it.