The Project Explorer shows all the entities contained in the project : Worlds, PHX (physics files) and configurations.
The Explorer panel shows all entities contained in the project. The firsts tree-nodes Worlds, Physics and Configuration are created by default: they are the three simulation main part.
Every element owns its contextual menu. The mouse double-click opens the document if the node refers to a document or select the entity in the current view if the node refers to a entity.