Java setup
Create a dedicated installation
In the Minecraft Launcher, open Installations → New and choose a release in the supported range 26.3–1.21.11. Give it a clear name such as Unstable SMP so you do not launch the wrong version by accident.
Keep your worlds separate
A new profile shares the same game directory by default. That is usually fine, but you can give this installation its own folder if you want to test mods or resource packs without touching your single-player worlds.
Join the server
Start the installation, open Multiplayer → Add Server, and enter unstable-events.net. Save the entry so the address and version stay together for the next session.
Need the address immediately? Open the server IP reference. For menus and setup, follow how to join Unstable SMP.