The Proto.io UI components are graphical elements designed to simulate the basic mobile OS UI elements. There are three collections of components: Basic, UI, and Templates. You can switch between collections by clicking on the relevant tab.
Switching between Libraries and Inspector is handled automatically depending on what you do. If you need to bring a series of UI components in your canvas, you can Pin the Libraries tab for convenience. The following dropdown (see on the right, below) appears under Device libraries.
Components can be added to the canvas either by dragging and dropping them on the canvas or by double-clicking on the component icon. When a component item is added to the canvas, a relevant layer appears in the Layers list and the Properties and Interactions Inspector appears for you to edit the size, position, properties, and interactions (see Properties inspector).