Time for action — going into Edit Mode
The difference between Object mode and Edit Mode is a little confusing at first. You look at the cube, and it's hard to tell which mode is which. But don't worry, you'll get the hang of it quickly enough.
Open up Blender, or select New from the File menu. Zoom into the cube, so that it fills up most of the 3D View. You are going to look at it in more detail.
Now press the Tab key. Press it several times. Note the changes in the 3D View, and the changes in the 3D View header.
What just happened?
You opened up Blender, and zoomed into the default cube. Then, you pressed the Tab key to go into Edit Mode. Edit Mode lets you modify parts of an object; the vertices, edges, and faces.
Both, Object Mode and Edit Mode, are shown here. In Edit Mode, you see dots at every corner of the cube, and all the edges of the cube are highlighted in orange. In the header, the Mode Selector button changes from Object Mode to Edit Mode, and some of the buttons change. Observe...