@Sarah
There are also some standalone "sims" you can run on your PC if it's only for experimenting without the need to connect to a grid. Opensim can do this, easier is to use a ready made and ready to run package like realXtend or 3DX for Windows. At least 3DX may not work anymore with a normal viewer, but haven't checked for a while. Best to stick with something
SL/Opensim compatible.