Essential Second Life Elements
Becoming an SL resident represented by your own avatar and spending time in the SL world is mandatory for anyone seeking to do serious SL development. In a real sense, you can think of time spent in SL as participating in a living, evolving operating environment for which you are creating artifacts often backed by your code. The more time you spend participating in SL, the better you understand the capabilities and limitations of SL's simulation and rendering engines. An interesting concept for developers is that you're living both inside an application and an IDE. Whenever you are in a coding mood, you press the Build button at the bottom of your screen and invoke the IDE.
You first need to download the SL client for your platform. There are clients for Windows, Mac OS X, and a Linux Beta. After installing, you create an identity (an avatar) for yourself. Every new avatar inherits a collection of objects, given to you by Linden Lab. Everything else you own has to be purchased or created by you or another resident.
When you create objects, you can hold them in your inventory, which is infinitely expandable and can stretch to hold your entire virtual clothing collection (plus an antique oak armoire to store it in). Of course, as your virtual storehouse gets bigger, the database fetch needed to populate it takes longer each time you connect with SL. There are techniques for compressing your holdings, but the best thing for you to do is to buy virtual land in-world.
If you buy and hold virtual land in SL, you can place whatever you want there and it remains. This rule applies to items you purchase or create. Thus, for example, even though your library of objects may contain interesting items and although you may create artifacts, you need to acquire land to give them permanent presence. This is how thousands of residents have created commercial revenue-producing sites that vend fashions, automobiles, and other virtual artifacts.
After going in-world, it is recommended that you teleport to one of the sandbox areas to build and test objects of your own creation in a sandbox. Then copy them into your inventory.
Because all sandboxes are wiped twice a day, make sure to copy your creations back into your inventory periodically ("save early, save often").
You can only create objects using in-world building tools (there are persistent rumors that eventually you'll be able to import external models), but you should create animations externally using Avimator (avimator.com), then import them in-world. You can use the syntax coloring editor in the object builder IDE, or use an external text editor (plug-ins exist for several popular ones).