A core element of the Blender user interface is the 3D Cursor, which is
that small crosshair icon that you will see in the 3D Viewport. The Cursor
has an essential role in the use of Blender (Figure 1.18).
Figure 1.18 - 3D Cursor
With the 3D Cursor you can:
Set the location where you create 3D objects
Move objects to a certain location
Work as a temporary pivot point for rotation and scaling
Those are a few functions for the 3D Cursor, which you use a lot for
modeling and object manipulation. Since that is a core function of
Blender, you must learn how to move and align the Cursor around the
3D Viewport.