When you make selections in the Pro interface, there's a multitude of ways that you can temporarily store that selection to isolate it and further narrow it down or contribute files to it. Learn more in this topic.
Adding assets to the pin bar
Having made a selection of files you can drag the entire selection to the pin bar at the bottom of the screen to store them there temporarily. This way you can add more assets to the selection before dragging it to an output for processing, and you can remove assets you choose not to keep.
Removing individual pinned assets
To remove an asset from the pin bar, click on the x that shows when you hover over the thumbnail in the pin bar.
Reducing the selection further
Having added a number of assets to the pin bar, you can drag the entire selection to a new tab above the grid by clicking and dragging the pin itself. This way the entire selection is displayed as thumbnails in the grid, and you can work with these as if they were in a regular archive. For example, you can change into filmstrip view or preview mode to further scrutinize pictures in your selection.
Having made a new selection from the original one, you can drag these assets to a new tab to reduce the selection further.