From BlenderWiki

Modeling in Blender

As you have seen in the Quick Start chapter, the creation of a 3D scene needs at least three key things: Models, Materials and Lights. In this Part we will delve deeper into the first of these issues Modeling. Modeling is the art and science of creating a surface that mimics the shape of a real-world object or fits your imagination of abstract objects.

Objects come in many forms, shapes and sizes, so Blender has many different tools available to help you make your model quickly and efficiently:

Objects

Working with objects as a whole.

Meshes

Working with the mesh that defines the shape of an object.

Curves

Using Curves to model and control objects.

Surfaces

Modeling a NURBS surface.

Texts

Textual tools for putting words in 3D space.

Metas

Globs and Globules.

Duplications

Duplicating Objects.

Modeling Scripts

Since Blender functionality is extensible via Python, there are a number of very useful scripts that assist you in modeling.

Many people use “box modeling” which starts with a basic cube, and proceeds with extruding and moving vertices to create a larger, more complicated mesh. For flat objects, like walls and table tops, you can use “curve modeling” which defines the outline using Bézier or Nurbs curves, and then extrudes it to the desired thickness. Either method is fully supported in Blender using its modeling tools.

Object and ObData Datablocks

The concept of “datablocks” is explained in details in the Data System chapter. However, to work well with Blender, it is absolutely crucial to understand the differences between the Object datablocks and the ObData datablocks, so let’s talk again about it here.

An Object datablock is a “container”. All types of objects (meshes, curves, metaballs, lamps…) are only usable in Blender when they are wrapped inside an Object datablock. This one defines also some common properties, available for all types of objects, like their location, size and rotation. You work on Object datablocks when you are in Object mode and/or using the Object context (F7).

As for the ObData datablock, it is the “real” object, containing all data describing it (the vertices/edges/faces for a mesh, the control points for a curve, etc.). You can only access an ObData datablock when it is used by one or more Object ones. You work on ObData datablocks when you are in Edit mode and/or using the Editing context (F9) (and sometimes a few other, more specific, modes, like e.g. Weight Paint or Sculpt modes, for meshes).

Note that “contexts” and “modes” are two “parallel” things, i.e. you can perfectly be in Edit mode, and still do some “object” operations using the tools in the Object context (and vice-versa, of course).

Another thing to mention is that, contrary to what one might think, a given object cannot hold any type of ObData – in fact, it is in general limited to one type (i.e. you have mesh objects for mesh ObData, camera objects for camera ObData, and so on).

As a final word, let’s mention constraints and modifiers. Both are tools that are designed to do non-destructive editing, respectively on Object and ObData datablocks. They are fully documented later on in this manual, but it is important to grasp them in this overall picture too.