The Selection menu provides the tools for selecting objects and controlling selected ones.
All
Selects all objects, cameras, and lights in the scene in Object mode. All points of a selected curve or surface in Edit mode.
All geometry
Selects all the objects in the scene.
All lights
Selects all the lights in the scene.
All cameras
Selects all the cameras in the scene.
None
Deselects a) all the objects in the scene if you are in Object mode, b) all the control points of selected objects if you are in Edit mode.
Invert
Swaps the selection of objects or points according to the working mode.
Group
Groups the selected objects into a more complex object so that any transformations can be applied to all of them at once. Grouping objects is also useful to put in order your scene.
You can select a group by simply picking it from the World Browser. If you create a new object while a group is selected, the object will be added to the currently selected group.
You can move an existing object into a group by just clicking and dragging it. To simply copy the object into a group, instead of moving it, click and drag it while pressing the left mouse button and the Ctrl key simultaneously.
Once you have selected a group of objects, you can move it, rotate it, or scale it by clicking in any view in a point free of any item and dragging with the mouse.
Ungroup
Separates parts of a group that you can select from the World browser.
Center in view
Centers selected objects in the active view so that only selected components are displayed.
Center in all views
Centers selected objects in all orthographic views so that only selected components are displayed.
Hide from rendering
Disables the rendering of selected objects. Once hidden from rendering, selected objects are transparent but already pickable.
Hide from view
Disables the visualization of selected objects in the views. Selected objects are hidden only after you deselect them. Once hidden from views, they can be selected again through the browser.