Occupying most of your screen space, the viewport utilizes Physically Based Rendering (PBR) to help you texture your assets. It is a 3D space where you can pan, rotate, and zoom to navigate around your 3D modal, as well as paint on them. You can also toggle the render modes and viewport controls within this left panel to help visualize the model and the results in various settings.
You can switch to the local library to see your saved and downloaded assets.
Or use the online library to acquire newer ones. Search and Filter features help you find the assets you are interested in.