You can begin using OpenSim immediately after installation.
To launch OpenSim on Windows:
Starting with OpenSim 4.0, the first time you launch OpenSim on Windows, you will likely see a Windows Security Alert. The operating system provides this alert because OpenSim contains a web browser. However, OpenSim does not use the web browser to access the internet (the browser is used only for local visualization). Click Allow access.
To launch OpenSim on Mac, navigate to your Applications folder, find the OpenSim folder, then click on the OpenSim icon.