(To see more pictures from Second Life, reload the page. If you don't see pictures, please enable Javascript.)
Second Life® is a multi-player online virtual reality environment. It's not really a game, because there is no plot, no story, and the goals are totally determined by the individual , just as they are in Real Life. So you can shop, or spend the night dancing in a club, or wander around in a park, or play a game, or visit a museum, or take a class, or run a shop, or build things, or garden, or decorate your dream home, or design clothing, or just sit and talk with your friends; it's all up to you.
All the content (everything you'll see "in world") is built by the residents (that's the people who go there, like you or me, not the company) using tools provided by Linden Lab (that's the company.)
If you want to make animations, sounds, or textures you'll need a separate program to do that. These things can be imported into SL, but not made there. However, there are free programs that will do what you need, such as the GIMP, for graphics, or DAZ Studio for animations.
But you can pretty much build anything you can imagine.
You can also be anything you want to be. You can be yourself. Or you can be a dragon, or a mermaid, or a griffin, or a 2 foot tall talking fox, or a furry, or a robot, or a horse, or a leopard, or an elf, or a flying plate of spaghetti, or a plywood cube. Or you can be a human child, or an old person, or change your gender or race with a couple of mouse clicks.
Whatever your shape or Avatar (the form you take,) you can fly, teleport and create things out of thin air. Which is just plain fun, really.
There is a great deal of creativity and beauty there, and a whole lot of really friendly people. Of course, it's not all roses, since the Residents are just people, and not all people are polite; but I have found that the fun parts far outweigh the not-fun bits.
The currency used in world to buy and sell things is called Linden dollars (L$) and generally runs about L$275 to $1 US; although this fluctuates. You can buy Lindens to spend, or you can earn them by providing goods or services in world. If you earn a surplus, you can "cash out" by selling your Lindens for actual currency.
Sound like something you'd like to try? You can join Second Life for free, and play for as long as you'd like (years, if you are so inclined,) without spending a cent.
If you want to look me up in world, I'm Robin Sojourner there.