The main Second Life website, where you can learn more about it, register for it, and download the software, is here:
There is, unsurprisingly, a thriving on-line community surround Second Life. I am a regular visitor to one of the main (unofficial) forums, SLUniverse, a site which also hosts the excellent Snapzilla, where you can post and share your snapshots of the world:
If you really get into it, sooner or later you will want to buy (and maybe sell) stuff. This can be done in-world, of course, but the SL Exchange website is perhaps a better way to track down precisely what you are looking for:
Finally, some shameless self-publicity -- you will find my own Second Life blog, hosted by Wordpress, here:
Second Life and Linden Lab are trademarks or registered trademarks of Linden Research, Inc. All rights reserved. No infringement is intended.