An important ingredient in OpenSim and Second Life is scripting.  In Second Life LSL (Linden Scripting Language) is the language you have to use.

OpenSim supports LSL, OSL and C# scripts. But with limitations:

• Not all commands and events have been implemented. See LSL Status for details on what commands work and which don't.
• Scripts that are running cannot cross region borders.
• You cannot use loops inside your scripts. Actually you can use loops, but it will block other scripts from executing.

The OpenSim script engine compiles the LSL code down to .Net code that is JIT'ed to CPU native code. In effect this means that a LSL script in OpenSim should run faster than in Second Life. Stability and security: see Script Execution Sandbox.

For more information about LSL and tutorials to learn LSL take a look at the LSL wiki

For more details about scripting in OpenSim take a look at the OpenSim Scripting Documentation