Blocking In - Blender Master Class: A Hands-on Guide to Modeling, Sculpting, Materials, and Rendering - page 32

In Edit mode, the W key brings up a menu with
a lot of handy tools for modeling. All of the opera-
tors you will use in Edit mode can be found in the
3D Viewport. As of Blender 2.5, when you use most
operators, the Tool Options panel will appear at the
bottom of the Tool Shelf, allowing you to change,
retroactively, the parameters of the operator you
just used. For example, after applying the Subdivide
operator, you can use the Tool Options panel to
change how many subdivisions to apply and whether
to smooth them.

other ways to Model: Curves
You can use Blender to create models in a number
of different ways, including using various curves,
metaballs (which behave somewhat like blobs of
clay that stick together when they get close to one
another), NURBS surfaces (surfaces constructed
from cross sections defined by curves), text objects,
and Bézier curves. Each has its place in modeling,
but the most important (after meshes) are Bézier
curves, which we'll use often throughout the model-
ing sections of this topic.
Bézier curves define a path in 3D space and
are constructed using control points and handles.
They can be used to make both wire- or ribbon-like
objects that follow the path of a curve (using closed
or open curves) and flat surfaces that are defined by
their outline (using closed 2D curves). Each control
point has two handles that define how the path flows
through that vertex, allowing you to create a wide
array of smooth and sharp paths with a curve.
Modeling with curves works very much like
using meshes; you can grab, rotate, scale, duplicate,
and extrude control points or their handles. (You
can't make faces from curves, though; you can only
connect each vertex in a curve to two others.)
When working with curves bear the following
in mind:

Figure 4-3: The Object Data tab for a curve object
allows you to change between a 2D and 3D curve,
set the density of the mesh created from that curve
(Resolution), and define how the curve is beveled
and extruded to create a 3D object (Geometry).

Curves can be open or closed. To close a curve,
select its two ends and press F to join them.
You can delete a segment of a closed curve by
selecting two or more connected points and
choosing X 4 Segment to make it open again.

Curves can be either 2D or 3D. Points on a 2D
curve cannot be moved along the curve object's
z -axis, which allows you to create a flat object by
defining its outline with a curve. Blender then
fills in the shape with faces according to the Fill
setting (see Figure 4-3). You can then extrude
the outline of a closed curve to create a solid
shape using the Geometry settings in the Object
Data tab. You can also add details like beveled
edges and change the curve's resolution here.

The geometry generated by curves is procedural .
This means that the curves you define are used
to generate a mesh according to the settings
you apply to the curve in the Object Data tab
(Figure 4-3) of the Properties editor. You can
change things like the number of divisions per
curve segment and the beveling and extrusion
applied to the curve.