You can see the basic UI components in the image below. These are components that are frequently used and are not specific to a certain operating system.
When you want to include a specific user interface (UI) component in your design, you just need to drag it onto your canvas or double click on it in the Library.
As you pick it up to drag, you will see a red circle on the top left corner of the component (a), which will turn green as soon as your component enters the canvas area and therefore you can drop it (b).
When you drop your component onto the canvas the Inspector tab opens for you to edit properties and interactions. (See Properties Inspector). At the same time, a relevant layer is added to the Layers list. The blue square handles that appear around the component allow you to quickly resize and rotate.