By Martin Kleppmann
The geometry of a Blender scene is constructed from one or more Objects: Lamps, Curves, Surfaces, Cameras, Meshes, and the basic objects described in Section 6.1. Each object can be moved, rotated and scaled in ObjectMode. For more detailed changes to the geometry, you can work on the mesh of an Object in EditMode (see Section 6.2).
Once you've added a basic object via SPACE>>Add menu, Blender changes into EditMode by default if the Object is a Mesh, a Curve or a Surface. You can change to ObjectMode by pressing TAB. The object's wireframe, if any, should now appear pink, meaning that the object is now selected and active.
Relevant to Blender v2.31
To select an object, click it with the RMB. To select multiple objects, hold down SHIFT and click with the RMB. Generally, the last object to be selected becomes the active one: It appears in light pink, whereas the non-active selected objects appear purple. The definition of the active object is important for various reasons, including parenting.
To deselect the active object, click it again with RMB, if multiple Objects are selected hold SHIFT to maintain the other selected. Press AKEY to select all objects in the scene (if none are currently selected) or to deselect all (if one or more is selected).
BKEY activates Border select. Use Border select to select a group of objects by drawing a rectangle while holding down LMB. You will select all objects that lie within or touch this rectangle.
Border select adds to the previous selection, so to select only the contents of the rectangle, deselect all with AKEY first. Use MMB while you draw the border to deselect all objects within the rectangle.