If you try to set a Z coordinate value of the Cube to zero, it will become

aligned to the "ground level" of your scene.

You can also use this same technique to place objects in the scene. For

instance, we easily place a Cube with an origin point at their bottom face

on top of another Cube or any other objects. Make sure the 3D Cursor is

at the same location in which you want to align the object to use this

procedure.

In that case, we have the Cube with the origin point at the bottom and

another larger Cube with the 3D Cursor aligned to the top face (Figure

2.21).

Figure 2.21 - Cubes for alignment

Select the Cube you wish to move and press SHIFT+S and pick

Selection to Cursor. It makes the selected Cube jump to the 3D Cursor

location (Figure 2.22).