Run the installer, read and accept the terms, choose what to set up, and click Install. It takes a few seconds.
Windows says it doesn't recognise the app? Yosh is new and its installer is not yet code-signed, so Windows SmartScreen or your antivirus may ask before running it. Check that the SHA-256 above matches your file, then choose More info and Run anyway. More help
Check your download (optional)
In PowerShell, run this in the folder you saved the file in, and compare the result with the SHA-256 above:
There is no macOS or Windows-on-ARM build yet. Archives are the same on every system, so a .yosh file made on Windows opens with the Linux tool and back again. Tell us which build you need.
Updating
The installer version checks once a day and updates itself, unless you turned that off. To update by hand, run the new installer over the old one; your settings are kept.
Uninstalling
Settings, Apps, Yosh Compressor, Uninstall. Your .yosh archives are never deleted.