Interfaces are anything that is displayed in the blender UI (user interface). This is everything from panels to pie menus.
You can create most of these with Serpens. There are some elements like panels for which you can choose a location. Other elements like menus can only be displayed with a shortcut or another node like a submenu.
Interfaces are represented by the yellow diamond socket. They are program sockets, meaning they follow a path from left to right, starting at a trigger node like a panel or menu.
The order the nodes are in represents the order the UI elements will be displayed. The actual elements that get displayed like labels, buttons or properties don’t have an interface output. If you want to place elements next to each other or change the general flow of the interface use row, column, box, or split nodes.
Nodes that display blender data have one or more property inputs. These are explained in detail in Blend Data and Properties.
You can write scripts to create interfaces. These will update live as you edit them, even in an external editor.
Interface functions can be used to reuse nodes instead of copying them. You can pass data into the function to do different things for the different run function nodes.
You can use logic nodes like If or For to display parts of the interface only in some cases or repeatedly, for example for every object in the scene.
Errors
Sometimes you will notice that elements after some element aren’t getting displayed. This is most likely because you have an error in your interface. Blender will not draw anything after this. Check the system console to see where these errors are coming from.