How do I download the Creta Launcher?

Go to Platforms → Multiverse. The download button is in the first section and again at the bottom of the page. It detects your operating system, so it reads Download for Windows or Download for macOS, and offers the other one underneath.

If you see no download button at all, no build has been published for your platform yet — the page only ever offers a release that exists. Windows and macOS are the two supported desktop platforms; there is no Linux build, and the launcher is not a phone app.