To start learning to build in Second Life, you should have some experience in Second Life. Let's say 40 hours. You should know how to look at things, how to shop, how to change clothings.
Some land you cannot create objects (or put down items). Places that do not allow build will have a stop-sign over a wooden box right beside the location's name in the top bar of your screen.
Here's what these signs mean. While in-world, you can double click them to get a explanation. (With Second Life Viewer 2 released in 2010, it no longer show these icons. There's a major user interface change. So, your menu and dialog boxes may look slightly different, however, the building tools features is the same.)
To get more information about a land, go to the menu 〖World ▸ About Land…〗 or clicking on the land's name in the menu bar. You'll get a info dialog. Under the Options tap, you can see a detailed info about the land's status on object creation.
A object has many properties and info associated with it. For example, its creator, owner, whether it is copyable, and its exact position coordinates, size, texture image, and so on. To find these details or edit them, click on the more button: .
After clicking on the “More >>” button, you'll get a lower panel with 5 tabs. This lower panel will be the same regardless whether you are in Create or Edit or any other mode. In the following, we explain each tab.
Congratulations. If you have come to this point, that means you have the basic building skills, you know all the construction tools, and you are technically able to build anything that can be built.
Eyes, face, skin are just bitmap image files mapped to the body. You start with a image template, and paint on this template (using a image editor like Photoshop or Gimp), upload it to Second Life to have a texture file. Then, use the in-world character editor to choose the image map. So, mostly, it requires image editing skill, and lots of trial and error.
To get the templates for these, go to: http://secondlife.com/community/templates.php
Underwear, body-tight clothing (socks, underwear), tattoo, are also done with bitmap images.
Most good-looking hairs, are made of flexi prims attached to a bald head. Similarly, good looking skirts, cloaks, shoes, are all made with prims. Hats are usually made together with hair. All these requires 3D-construction skills.
Poses and humanoid movement animations are made with a specialized file format called BVH. The BVH file specifes human posture and movements. To generate this file, you can use a Motion capture system, or use a software that specializes in generating humanoid animations. Namely: Poser, Maya (software), Blender (software) (free), http://www.qavimator.org/ (free), and others.
For a basic intro, see: http://wiki.secondlife.com/wiki/Animation.
For making a vehicle that people can drive, or teleporter, shooting weapons (guns, bows and arrows), fighting systems (swords, light saber), shooting fireworks, and much more, you'll need to know how to script. See Linden Scripting Language Tutorial.
There is a in-world tutorial called The Ivory Tower Library of Primitives, at Natoma (203,166,27). It is created by Lumiere Noir. I learned many tips from his tutorial.