The process of selecting objects is very important to manipulate and transform objects in any 3D package. To select objects in Blender, we have options to use the mouse and to select objects by name. If we want to select a single object, just click with the right mouse button over this object, and it will be selected. To add another object to the selection, just press Shift and click with the right mouse button over another object.
In Blender, the mouse buttons work in a different way. In most 3D applications, the left mouse button selects one object. But with Blender, the right mouse button selects objects. If you find it confusing, it can be changed in the User Preferences.
The A Key is a very important tool ...