Components are structured groups of elements that can be reused throughout your project. They live in the Library of your project and can be retrieved from there for use on any page.
To create a component, select the elements that will make up the component and use the commandElement > Create Component or ⌘+K Ctrl+K. You will be asked to name the new component after which the component will become available in your library. You can then create a new instance of the component by dragging it from the library to the canvas.
Note: The name you enter for the component will be used only for reference within the library. It will not affect the markup in any way.