A Scene is used to associated Colliders, Emitters and Solvers with each other.
Colliders, Emitters and Solvers can either link directly to a scene anywhere in your document or you can make these a child of the Scene Object.
By setting the linked scene directly in the Colliders and Emitters it allows those tags to be attached to any animated object in your Object Manager. When the solver starts caching it will look for all the coliders and emitters that are associated with the same scene that the solver is.
You can have multiple sovlers all referencing the same scene, allowing them all to use the same coliders and emitters. This lets you run simulations using different solvers with the abillity to compare the results directly.
Pressing any of the buttons will add a solver as a child of the Scene Object. It will also link the solver to the scene itself.