Owlet comes with a library of materials and images that you can use to speed up your scene setup. There is a panel called Materials Library that contains all the materials that come with Owlet:
There is a filtering box at the top of the panel and a drop-down control that helps you filter out materials by their types. Then comes the long list of materials grouped by type (metal, glass, plastic, paint and so on), there are also images there, like textures and HDR environment images.
You simply pick the material you need and drag it onto the shape you need. The material is assigned to the shape and automatically added to the scene materials list. You can also drag materials directly into the scene materials list and then assign them from there.
The same applies to the images from the library, but instead of dragging them onto shapes or into the scene materials list, you need to drag them onto the texture controls of either material or scene properties editors.