Wall/Wall Shadow and Interfaces
 

Hello, I'm a bit confuse regarding the wall/wall-shadow and interface at the same time. I want to follow the Boundary Condition.png but they have both wall/wall-shadow
At Geometry I put the mode, as "Form New Part". If my understanding is correct, this should make all the parts in the model to automatically contact each other like a share topology.
But at Meshing I need to make wall-e (fluid to fluid surface) so wall and wall shadow is form. But there is also some part I need to make as interface (fluid-fluid surface). If I put as in Name Selection.png, I need to Mesh Interface at Setup Fluent but I cannot do that.

Any solution to my problem? Can you understand what I'm trying to say?