Favorites, or Tray in the Daminion Web Client allows you to create a temporary selecting of files from different searches to be shared or exported to PDF later on.
To add a file to the Favorites, hover your mouse over a thumbnail and click the heart icon.

Once at least one file is added to the Favorites, an additional icon appears in the toolbar.

Click the heart icon in the toolbar to display the contents of the Favorites.

Here you can select your files to download them, create a shared collection, or export them to PDF.