The Assets library provides an easy way to access and organize the external files (images, video, widgets, etc) used in the UI composition.
By default the assets library automatically lists the files located in the following folders located in the directory of the html file of the composition: images, videos, widgets.
If you wish to import addition assets you just need to click on the "plus" sign next to the asset time and from the popup menu to choose the asset and where it will be saved.
Previewing assets in the library is very easy - simply click on the asset in the list and you'll see it's visualization in the preview window. This is especially useful for video and animated widgets elements that are automatically played in the preview window.
Adding assets to the scene
To add an asset to the scene you can use drag and drop from the library to the scene. While dragging you'll see a visualization of the asset.