For general informations about the Blender user interface see the respective Blender handbook section.
After installation of BlenderBIM the default Blender start-up screen looks different from the standard Blender interface.
BlenderBIM adds a new BIM Workspace to the interface and by default activates this workspace on start-up. It also modifies the layout of views and sidebars and adds custom functionality to the toolbar. The left Outliner panel shows a tree of geometric objects. The centre main Viewport panel shows 3D geometry. The right Properties panel shows data and relationships.
BlenderBIM BIM workspace tab
Outliner with the document tree
Main 3D viewport
Toolbar with added BIM functionality
Status bar with information about the currently used Blender and BlenderBIM version
Additionally, the File menue in the Topbar adds menue entries to Create/Open and Save an IFC project directly.