Without Node or Bun
The curl line installs Loom on a machine that has neither Node nor Bun. On macOS or Linux, it puts Loom in ~/.loom/bin as a single file. It then adds that folder to your PATH, the list of folders your terminal searches for commands. It makes the change in your shell's profile, such as ~/.zshrc, and tells you which file it changed. Open a new terminal afterwards, so the shell reads the change.
If you'd rather edit your PATH yourself, end the line with sh -s -- --no-modify-path instead of sh.
On Windows
Download loom-windows-x64.exe.gz from the releases page, and unpack it with a tool such as 7-Zip.
On macOS
Apple hasn't signed or notarised the macOS file yet. Installed with curl, it runs straight away. Downloaded through a browser, it won't open until you allow it in System Settings.
When an older loom answers
If loom --version prints an older version than the one you installed, a loom from an earlier install, with npm or Bun, may come first on your PATH. The install script names any it finds.
checks again at any time. It shows which loom your terminal runs, lists every other one with the command that removes it, and checks the project you run it in.