For what are those Silver balls.

For what are those Silver balls. How to use them and why?

They are reflection spheres https://docs.unrealengine./latest/INT/Resources/ContentExamples/Reflections/1_4/index.html

They are reflection capture actors. They capture environment within their bounds and materials use those for reflections. For interiors you usually need box reflection captures for each room and spherical captures for more detailed, localized reflections.

For future reference, you can select any Actor in Viewport and view it in World Outliner. This will display Actor Name (Label) and its Type. Then you can use the documentation to research it further.

Hope that helps!

In what cases we use it and in which places.