Depending on how organized you want your scenes to be, eventually you will need to use the Outliner. If you go to the bottom-left of any view, you can click the Editor Type drop-down menu and choose the Outliner (or press Shift + F9 while hovering in a view).
The Outliner shows the scene hierarchy (Figure 1). At the top of the hierarchy is the Scene, but you can also have multiple scenes within the same file. In a scene with the default cube, the scene hierarchy is expanded to show Render Layers, World, Camera, Cube and Lamp.
Click to expand the Render Layers section of the Outliner (Figure 2). Render Layers are for compositing your scene. You may "check" these layers on or off by clicking on the boxes to the right. This will have the same effect as toggling passes using the Layers of the Render panel. To save space, close the Render Layers hierarchy when you're done looking at it.
"World" is the default name for the world of the current Scene. It holds all the properties for the scene's environment, but you cannot seem to select it. Instead, you can go to the Properties panel and select the "earth" icon to edit the World properties.
If you LMB-click on the Camera, Cube or Lamp in the Outliner, their names will highlight in white and each will toggle being selected in your view. If you select multiple Objects, the Active Object will also be the one with the white highlight in the Outliner. Hit the <Home> key to frame all objects in your view to see each selected as you click their names. These are all Objects, and they will always be at the top level of the hierarchy.
The Object icons are orange in color but are different shapes depending on the Object type. For example: Mesh Objects have an icon of a triangle with points on the corners, like a triangle in edit mode.
If you expand any of these Objects, the hierarchy will expand a little more. Nested beneath the Objects are the datablocks associated with those Objects.
Expand "Camera" to see another name of "Camera" with the same movie camera icon to the left. This is the Camera datablock; it holds the Camera options. Expand "Cube" to see another name of "Cube" with a triangle icon to the left. This is the Cube datablock; it holds the Cube mesh options. You may also toggle Edit Mode and Object Mode by clicking this mesh icon. Expand "Lamp" to see the name of "Spot" with a multi-directional light icon. The name of this datablock should actually be "Point"; hopefully it will be fixed before version 2.6 is released. This is the Lamp datablock; it holds the Lamp options (Figure 3).
Also note the Properties panel directly beneath the Outliner, by default. Along the top of this panel are several icons, some of which are context-sensitive. Select the camera and note that there is a "cube" icon and a "movie camera" icon among these. If you hover over the cube icon, "Object" will appear, and if you hover over the movie camera icon, "Object Data" will appear. "Object" is for Object properties, and "Object Data" is for datablock properties for the selected object.
The Object properties can also be accessed by hitting "N" while hovering in a view to toggle the Properties panel (Figure 4). This version of the Properties panel has some other properties as well, such as related to the view, but it still contains the Object name and transform info, just like the fixed panel.
If you select the field with the cube icon next to it and type in a new name, you will have just changed the Object name, and it will also change in the top-level of the Outliner. I selected the cube and renamed it to "box." You may also change the names directly in the Outliner. Simply CTRL + LMB-click on any name and enter a new name (Figure 5).
Select the camera again and click on the movie camera icon in the Properties panel to see the name of the Camera datablock as the same in the Outliner, also "Camera." This is where Blender can be initially confusing when dealing with datablocks; the default datablock for Cube is also "Cube."
You can view another tutorial on datablocks, but in general just remember the Object holds the transform information, and datablocks describe most other Object properties. All Objects will be unique because they have their own transforms, whereas the datablock will be linked to the Object and can have exact duplicates. If you make a linked duplicate of an Object, its datablock is shared.
If you expand the Cube down further, you will see "Material" on the next level. This is another datablock; it is linked to the Mesh level, because it's nested directly beneath it. And... if you expand the Cube down one more level, the "Tex" datablock (texture) is revealed. Since it is nested directly beneath Material, it depends on it. You can't have a texture without first creating a material (Figure 6).
Try this with Parenting was well. Select the Lamp, then the Cube and press CTRL + P. Then look at the Outliner: the Lamp is nested beneath the cube and now depends on it. Try this out with other functions within Blender to see the nesting effects.
Also notice on the far right of the Outliner are three icons: an eye, an arrow and a camera. The eye toggles visibility of your object in your scene. The arrow toggles the ability to select objects. The camera toggles whether or not your object will render.