Basics questions for architectural interface

hello i have a few questions im a beginner

1/ as in the image why do the sides look black when i play although they dont while editing, what can i change?
2/ theres this widget in middle that keeps appearing all tiime, what node makes it only show when its widget is opened?
3/ how do i create shadows from building on other objects that would change with sunsky slider ?
4/ any good tutorial to change materials using buttons ?