Interface elements are special elements that are attached to other elements and represent their inidividual network interfaces. They form a child-parent relationship with their parent elements.
The editor automatically creates and deletes interface elements with their respective connection. Interface elements are also deleted with their parent element.
Interface elements are represented by small circles around their parent elements. Note that you can interact with them via their right-click menu like you can interact with any other elements.

If the interface is not visible on your connections, make sure that Connection Controls are enabled in the editor’s Options Menu tab.
Interface elements do not support actions themselves. They change their states automatically with their parents.
Configuration options highly depend on the device type of the parent device. Please refer to the specific manual page (Container, Full, Repy) for more information.